CRC · California Residential Code
What are the interconnection and power/backup requirements for smoke alarms?
For homeowners: if your house work or new construction requires more than one smoke alarm, the alarms must be UL‑listed, installed per the manufacturer, and interconnected so one alarm makes them all sound. In new construction (or when the code otherwise requires), alarms must be hard‑wired to the house electrical system with a battery backup; limited exceptions allow battery‑only alarms in some existing, non‑construction situations. See § R310.4, § R310.1.1 and § R310.1.2 for interconnection, listing and installation rules and § R310.6 for power/backup specifics .
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
- Smoke alarms installed where more than one is required in a dwelling or sleeping unit must be interconnected so that when one alarm activates all required alarms in that unit activate and are clearly audible in bedrooms with doors closed (§ R310.4) .
- Smoke alarms must be listed (UL 217) and installed in accordance with their listing and the manufacturer's instructions (§ R310.1.1, § R310.1.2) .
- The CRC’s power/back‑up rules are stated elsewhere in the Smoke Alarm section: required alarms in new construction must receive primary power from building wiring served from a commercial source and must be equipped with a battery backup; wiring must be permanent (see § R310.6) .
The single most important practical rule: if your project requires more than one smoke alarm in a dwelling unit, they must be interconnected so a single alarm sets off every required alarm in that unit and the alarms must be listed and installed per their listing and manufacturer instructions (see § R310.4, § R310.1.1, § R310.1.2) .
Requirements in detail
Key defined terms (first mention bolded)
- Interconnected — alarms wired or linked so activation of one causes all required alarms in the same dwelling/sleeping unit to sound (§ R310.4) .
- Listed — certified to the recognized standard (smoke alarms: UL 217) (§ R310.1.1) .
- Installed in accordance with their listing — mounted and wired exactly as the manufacturer / listing requires (§ R310.1.2) .
- Battery backup — on‑device or permitted battery power that supplies the smoke alarm when primary building power is interrupted (see § R310.6) .
Decision table — what to check and where the code says it
| Requirement | What it means (decision relevance) | When it applies | Code Reference |
|---|---|---|---|
| Interconnection of multiple alarms | One alarm activation must make all required alarms in the same dwelling/sleeping unit sound; audible in bedrooms with doors closed | Where more than one smoke alarm is required in a dwelling/sleeping unit | § R310.4 |
| Listing / approval | Smoke alarms must be listed and labeled to UL 217; combo smoke/CO alarms to UL 217 & UL 2034; SFM listing where required | All smoke alarms | § R310.1.1 |
| Installation standard | Installations must follow the alarm’s listing and manufacturer instructions | All smoke alarms | § R310.1.2 |
| Primary power / backup | Primary power from building wiring served from a commercial source; battery backup required; wiring permanent (no disconnect) | Required in new construction and where required by other sections | § R310.6 |
| Low‑battery indication | Alarm must emit a signal when batteries are low | Where battery backup is provided | § R310.6 |
| Wireless alternative for interconnection | Listed wireless alarms that cause all alarms to sound are acceptable instead of physical wiring | When listed wireless alarms are installed and function as required | (Referenced in the CRC and Fire Code interoperability text) § R310.4 and related fire code text |
| Exceptions allowing battery‑only alarms | Where no construction is taking place, buildings without commercial power, or certain limited alteration situations | Existing buildings not undergoing work or limited scope repairs (see enumerated exceptions) | § R310.6 — Exceptions 1–5 |
Notes: the CRC text controlling definitions and listing/installation are § R310.1.1 and § R310.1.2; the functional interconnection rule is § R310.4; the code’s explicit power and battery‑backup language is in § R310.6 (the CRC lists the power requirements there) .
Audible requirements
- The alarms must be clearly audible in all bedrooms over background noise levels with intervening doors closed when one alarm activates (§ R310.4) .
- Special occupancies (e.g., certain Group R-3.1 facilities) have additional dB audibility specifications in the Fire Code (see related provisions below) .
Exceptions & special cases
- Interconnection is not required in buildings that are not undergoing alterations, repairs or construction of any kind (§ R310.4 Exception 1) .
- Interconnection is waived for existing areas where the work does not remove interior wall/ceiling finishes exposing the structure, unless attic/crawl/basement access would allow interconnection without removing finishes (§ R310.4 Exception 2) .
- For power, battery‑only smoke alarms are permitted in existing buildings where no construction is taking place, in buildings without commercial power, and in limited alteration/repair scenarios listed in § R310.6 Exceptions 1–5 .
- Listed wireless interconnected alarms that sound all units when one activates are permitted in lieu of physical wiring when the alarms are listed for that purpose (CRC and Fire Code recognize listed wireless options) .
If you need to rely on wireless interconnection as the method of compliance, verify the specific product is listed for wireless interconnection and that the installation meets the device listing and manufacturer instructions (§ R310.1.1, § R310.1.2) .
Common mistakes
- Assuming any off‑the‑shelf alarm that “talks” can be used for interconnection — only listed devices (and listed wireless systems) that meet UL/State listing for interconnection are acceptable (§ R310.1.1, § R310.4) .
- Installing battery‑only alarms in new construction or during permitted alterations where building power and interconnection are required — the CRC requires primary building wiring with battery backup except where exceptions apply (§ R310.6) .
- Cutting off the alarm’s permanent wiring with a local switch or using a non‑permanent connection — wiring must be permanent and without a disconnecting switch except as required for overcurrent protection (§ R310.6) .
- Not following the manufacturer’s listed installation methods (mounting location, spacing, airflow exclusions) — installation must follow the listing and manufacturer’s instructions (§ R310.1.2, § R310.3.3 references) .
Worked example — a concrete scenario
Scenario: Single‑family dwelling, new construction, three bedrooms, one on each corner of a single story plus a living room. You must determine interconnection and power/backup:
- How many alarms required? At minimum: one inside each sleeping room (3), one outside the sleeping area in the immediate vicinity (1), and one on each story (already same single story) — total: 4 required alarms per § R310.3 (location rules) .
- Interconnection: Because more than one alarm is required, all four must be interconnected so activation of any one causes all to sound and must be audible in each bedroom with doors closed (§ R310.4) .
- Power/backup: In new construction, each required alarm must have primary power from the building wiring served from a commercial source and a battery backup; wiring must be permanent and alarms must provide a low‑battery signal (§ R310.6) .
- Listing & installation: Use UL 217 listed alarms or combination UL 217/UL 2034 for combo units, and install per the alarm listing and manufacturer instructions (§ R310.1.1, § R310.1.2) .
So: use four UL‑listed interconnected alarms, hard‑wired to the household circuit with battery backup, or use listed wireless interconnected alarms if listed and installed per their listing; do not use battery‑only alarms in this new construction scenario (exceptions do not apply) (§ R310.6, § R310.4, § R310.1.1) .
Related provisions
- § R310.1.1 — Listings (UL 217; combo UL 217 & UL 2034) .
- § R310.1.2 — Installation per listing and manufacturer instructions .
- § R310.3 — Specific locations where smoke alarms are required (sleeping rooms, outside sleeping areas, each story) .
- § R310.4 — Interconnection requirement and exceptions .
- § R310.6 — Power source and battery backup requirements and exceptions (see enumerated Exceptions 1–5) .
- Fire Code / CBC references (for special occupancies and audibility): e.g., 907.2.11.6 (power) and 907.2.11.5 (interconnection) — for Group R specifics and audible levels in facilities .
If a particular project or occupancy (e.g., licensed care facilities, Group R‑3.1) is involved, consult the Fire Code / CBC sections listed above for additional power, audibility and visible‑notification requirements; the CRC incorporates these occupancy‑specific rules by reference .
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 7.1 High relevance — show source text
R310.4 Interconnection. Where more than one smoke alarm is required to be installed within an individual dwelling or sleeping unit, the smoke alarms shall be interconnected in such a manner that the activation of one alarm will activate all of the alarms in the individ- ual unit. The alarm shall be clearly audible in all bedrooms over background noise levels with all intervening doors closed.
Exceptions: 1. Interconnection is not required in buildings that are not undergoing alterations, repairs or construction of any kind. 2. Smoke alarms in existing areas are not required to be interconnected where alterations or repairs do not result in the removal of interior wall or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available which could provide access for interconnection without the removal of interior finishes. 3. Smoke alarms are not required to be interconnected where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 4. Smoke alarms are not required to be interconnected when work is limited to the installation, alteration or repairs of plumb- ing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
R310.5 Combination alarms. Combination smoke and carbon monoxide alarms shall be permitted to be used in lieu of smoke alarms. Systems and components shall be California State Fire Marshal listed and approved in accordance with California Code of Regu- lations, Title 19, Division 1 for the purpose for which they are installed.
R310.6 Power source. Smoke alarms shall receive their primary power from the building wiring provided that such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exceptions:
1. Smoke alarms are permitted to be solely battery operated in existing buildings where no construction is taking place. 2. Smoke alarms are permitted to be solely battery operated in buildings that are not served from a commercial power source. 3. Smoke alarms are permitted to be solely battery operated in existing areas of buildings undergoing alterations or repairs that do not result in the removal of interior walls or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available which could provide access for building wiring without the removal of interior finishes. 4. Smoke alarms are permitted to be solely battery operated where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 5. Smoke alarms are permitted to be solely battery operated when work is limited to the installation, alteration or repairs of plumbing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
R310.7 Fire alarm systems. Fire alarm systems shall be permitted to be used in lieu of smoke alarms and shall comply with Sections R310.7.1 through R310.7.4.
CRC § 9-31 High relevance — show source text
2025 CALIFORNIA BUILDING CODE 9-31
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FIRE PROTECTION AND LIFE SAFETY SYSTEMS
2. A manual fire alarm system. 3. Smoke alarms required by the California Fire Code Section 907.2.10.
907.2.11.2.1.1 Smoke alarms. Single- and multiple-station smoke alarms shall be installed in accordance with California Fire Code Section 907.2.11.
907.2.11.2.2 Group I-4 occupancies. Large family day-care homes shall be equipped with State Fire Marshal approved and listed single station residential type smoke alarms.
907.2.11.2.3 Group R-3.1. In all facilities housing a bedridden client, smoke alarms shall receive their primary power from the build- ing wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms shall be electrically interconnected so as to cause all smoke alarms to sound a distinctive alarm signal upon actuation of any single smoke alarm. Such alarm signal shall be audible throughout the facility at a minimal level of 15 dB above ambient noise level. These devices need not be interconnected to any other fire alarm device, have a control unit, or be electrically supervised or provided with emer-
gency power.
907.2.11.2.4 Smoke alarms. Smoke alarms shall be tested and maintained in accordance with the manufacturer's instructions. Smoke alarms that no longer function shall be replaced.
907.2.11.2.5 Existing Group R occupancies. See the California Residential Code for existing Group R-3 occupancies or Chapter 11 of the California Fire Code for all other existing Group R occupancies.
907.2.11.2.6 Group R-4. A manual fire alarm system that activates the occupant notification system in accordance with Section 907.5 shall be installed in Group R-4 occupancies housing nonambulatory clients.
[F] 907.2.11.3 Installation near cooking appliances. See Section 907.2.11.8.
[F] 907.2.11.4 Installation near bathrooms. See Section 907.2.11.8.
[F] 907.2.11.5 Interconnection. Where more than one smoke alarm is required to be installed within an individual dwelling unit or sleeping unit in Group R occupancies, the smoke alarms shall be interconnected in such a manner that the activation of one alarm will activate all of the alarms in the individual unit. Physical interconnection of smoke alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm. The alarm shall be clearly audible in all bedrooms over background noise levels with all intervening doors closed.
[F] 907.2.11.6 Power source. In new construction, and in newly classified Group R-3.1 occupancies, required smoke alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system in accordance with Section 2702. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
CRC § 1103.8.3 High relevance — show source text
Exceptions:
- Interconnection is not required in buildings that are not undergoing alterations, repairs or construction of any kind.
- Smoke alarms in existing areas are not required to be interconnected where alterations or repairs do not result in the removal of interior wall or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available that could provide access for interconnection without the removal of interior finishes. 3. Smoke alarms are not required to be interconnected where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addi- tion of a porch or deck. 4. Smoke alarms are not required to be interconnected when work is limited to the installation, alteration or repairs of plumbing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
1103.8.3 Power source. Single-station smoke alarms shall receive their primary power from the building wiring provided that such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exceptions:
- Smoke alarms are permitted to be solely battery operated in existing buildings where construction is not taking place.
- Smoke alarms are permitted to be solely battery operated in buildings that are not served from a commercial power
source.
- Smoke alarms are permitted to be solely battery operated in existing areas of buildings undergoing alterations or repairs that do not result in the removal of interior walls or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available that could provide access for building wiring without the removal of interior finishes. 4. Smoke alarms are permitted to be solely battery operated where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck.
11-10 2025 CALIFORNIA FIRE CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
CONSTRUCTION REQUIREMENTS FOR EXISTING BUILDINGS
5. Smoke alarms are permitted to be solely battery operated when work is limited to the installation, alteration or repairs of plumbing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
1103.8.4 Group R-3.1. In all facilities housing a bedridden client, smoke alarms shall receive their primary power from the building wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms shall be electrically interconnected so as to cause all smoke alarms to sound a distinctive alarm signal upon actuation of any single smoke alarm. Such alarm signal shall be audible throughout the facility at a minimal level of 15 db above ambient noise level. These devices need not be interconnected to any other fire alarm device, have a control panel, or be electrically supervised or provided with emer-
gency power.
1103.8.5 Additional provisions for existing Group R occupancies.
CRC § 7.1 High relevance — show source text
R310.6 Power source. Smoke alarms shall receive their primary power from the building wiring provided that such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exceptions:
1. Smoke alarms are permitted to be solely battery operated in existing buildings where no construction is taking place. 2. Smoke alarms are permitted to be solely battery operated in buildings that are not served from a commercial power source. 3. Smoke alarms are permitted to be solely battery operated in existing areas of buildings undergoing alterations or repairs that do not result in the removal of interior walls or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available which could provide access for building wiring without the removal of interior finishes. 4. Smoke alarms are permitted to be solely battery operated where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 5. Smoke alarms are permitted to be solely battery operated when work is limited to the installation, alteration or repairs of plumbing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
R310.7 Fire alarm systems. Fire alarm systems shall be permitted to be used in lieu of smoke alarms and shall comply with Sections R310.7.1 through R310.7.4.
R310.7.1 General. Fire alarm systems shall comply with the provisions of this code and the household fire warning equipment provisions of NFPA 72. Smoke detectors shall be listed in accordance with UL 268. Systems and components shall be California State Fire Marshal listed and approved in accordance with California Code of Regulations, Title 19, Division 1 for the purpose for which they are installed.
R310.7.2 Location. Smoke detectors shall be installed in the locations specified in Section R310.3.
2025 CALIFORNIA RESIDENTIAL CODE 3-55
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
�
BUILDING PLANNING
R310.7.3 Permanent fixture. Where a household fire alarm system is installed, it shall become a permanent fixture of the occupancy, owned by the homeowner.
R310.7.4 Combination detectors. Combination smoke and carbon monoxide detectors shall be permitted to be installed in fire alarm systems in lieu of smoke detectors, provided that they are listed in accordance with UL 268 and UL 2075.
R310.8 Existing Group R-3 occupancies.
R310.8.1 Group R-3 Effective Date. Existing buildings housing Group R-3 occupancies established prior to the effective date of these regulations may have their use continued if they conform or are made to conform to provisions of these regulations to the extent that reasonable and adequate life safety against the hazards of fire, panic and explosion is substantially provided. Additional means of egress, the installation of automatic sprinkler systems, automatic fire alarm system or other life safety measures, may be required to provide reasonable and adequate safety.
CRC § 0.91 High relevance — show source text
would prohibit the placement of a smoke alarm or smoke detector required by other sections of the code. Smoke alarms listed for use in close proximity to a permanently installed cooking appliance. (5) Installation near bathrooms. Smoke alarms shall be installed not less than a 3 foot (0.91 m) horizontal distance from the door or opening of a bathroom that contains a bathtub or shower unless this would prevent placement of a smoke alarm required by other sections of the code.
(6) Smoke alarms and smoke detectors shall not be installed within a 36 in. (910 mm) horizontal path from the supply registers of a forced air heating or cooling system and shall be installed outside of the direct airflow from those registers. (7) Smoke alarms and smoke detectors shall not be installed within a 36 in. (910 mm) horizontal path from the tip of the blade of a ceiling-suspended (paddle) fan. (8) Where stairs lead to other occupied levels, a smoke alarm or smoke detector shall be located so that smoke rising in the stair- way cannot be prevented from reaching the smoke alarm or smoke detector by an intervening door or obstruction. (9) For stairways leading up from a basement, smoke alarms or smoke detectors shall be located on the basement ceiling near the entry to the stairs. (10) For tray-shaped ceilings (coffered ceilings), smoke alarms and smoke detectors shall be installed on the highest portion of the ceiling or on the sloped portion of the ceiling within 12 in. (300 mm) vertically down from the highest point. (11) Smoke alarms and detectors installed in rooms with joists or beams shall comply with the requirements of 17.7.3.2.4. (12) Heat alarms and detectors installed in rooms with joists or beams shall comply with the requirements of 17.6.3.
R310.4 Interconnection. Where more than one smoke alarm is required to be installed within an individual dwelling or sleeping unit, the smoke alarms shall be interconnected in such a manner that the activation of one alarm will activate all of the alarms in the individ- ual unit. The alarm shall be clearly audible in all bedrooms over background noise levels with all intervening doors closed.
Exceptions: 1. Interconnection is not required in buildings that are not undergoing alterations, repairs or construction of any kind. 2. Smoke alarms in existing areas are not required to be interconnected where alterations or repairs do not result in the removal of interior wall or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available which could provide access for interconnection without the removal of interior finishes. 3. Smoke alarms are not required to be interconnected where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 4. Smoke alarms are not required to be interconnected when work is limited to the installation, alteration or repairs of plumb- ing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
R310.5 Combination alarms. Combination smoke and carbon monoxide alarms shall be permitted to be used in lieu of smoke alarms. Systems and components shall be California State Fire Marshal listed and approved in accordance with California Code of Regu- lations, Title 19, Division 1 for the purpose for which they are installed.
CRC § 907.2.11.2.3 High relevance — show source text
907.2.11.2.3 Group R-3.1. In all facilities housing a bedridden client, smoke alarms shall receive their primary power from the building wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms shall be electrically interconnected so as to cause all smoke alarms to sound a distinctive alarm signal upon actuation of any single smoke alarm. Such alarm signal shall be audible throughout the facility at a minimal level of 15 db above ambient noise level. These devices need not be interconnected to any other fire alarm device, have a control panel, or be electronically supervised or provided with emergency power.
907.2.11.2.4 Smoke alarms. Smoke alarms shall be tested and maintained in accordance with the manufacturer’s instructions. Smoke alarms that no longer function shall be replaced.
907.2.11.2.5 Existing Group R occupancies. See the California Residential Code for existing Group R-3 occupancies or Chapter 11 of the California Fire Code for all other existing Group R occupancies.
907.2.11.2.6 Group R-4. A manual fire alarm system that activates the occupant notification system in accordance with Section 907.5 shall be installed in Group R-4 occupancies housing nonambulatory clients.
907.2.11.3 Installation near cooking appliances. See Section 907.2.11.8.
907.2.11.4 Installation near bathrooms. See Section 907.2.11.8.
907.2.11.5 Interconnection. Where more than one smoke alarm is required to be installed within an individual dwelling unit or sleeping unit in Group R or I-1 occupancies, the smoke alarms shall be interconnected in such a manner that the activation of one alarm will activate all of the alarms in the individual unit. Physical interconnection of smoke alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm. The alarm shall be clearly audible in all bedrooms over background noise levels with all intervening doors closed.
907.2.11.6 Power source. In new construction, and in newly classified Group R-3.1 occupancies, required smoke alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery back-up shall be connected to an emergency electrical system in accordance with Section 1203. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exception: Smoke alarms are not required to be equipped with battery backup where they are connected to an emergency electrical system that complies with Section 603.
907.2.11.7 Smoke detection system. Smoke detectors listed in accordance with UL 268 and provided as part of the building fire alarm system shall be an acceptable alternative to single- and multiple-station smoke alarms and shall comply with the following:
- The fire alarm system shall comply with all applicable requirements in Section 907.
- Activation of a smoke detector in a dwelling unit or sleeping unit shall initiate alarm notification in the dwelling unit or sleeping unit in accordance with Section 907.5.2.
- Activation of a smoke detector in a dwelling unit or sleeping unit shall not activate alarm notification appliances outside of the dwelling unit or sleeping unit, provided that a supervisory signal is generated and monitored in accordance with Section 907.6.6.
CRC § 3.1 High relevance — show source text
4. In a Group R-3.1 occupancies, in addition to the above, smoke alarms shall be provided throughout the habitable areas of the dwelling unit except kitchens. See Section 907.2.10.8 for specific location requirements. 907.2.11.2.1 Licensed Group R-2.1 occupancies. Licensed Group R-2.1 occupancies housing more than six nonambulatory, elderly clients shall be provided with an approved manual and automatic fire alarm system. Exceptions: Buildings housing nonambulatory clients on the first story only and which are protected throughout by the following: 1. An approved and supervised automatic sprinkler system, as specified in Sections 903.3.1.1 or 903.3.1.2, which upon activation will initiate the fire alarm system to notify all occupants. 2. A manual fire alarm system. 3. Smoke alarms required by Section 907.2.11.
907.2.11.2.1.1 Smoke alarms. Single- and multiple-station smoke alarms shall be installed in accordance with Section 907.2.11.
2025 CALIFORNIA FIRE CODE 9-45
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FIRE PROTECTION AND LIFE SAFETY SYSTEMS
907.2.11.2.2 Group I-4 occupancies. Large family day-care homes shall be equipped with State Fire Marshal approved and listed single station residential type smoke alarms.
907.2.11.2.3 Group R-3.1. In all facilities housing a bedridden client, smoke alarms shall receive their primary power from the building wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms shall be electrically interconnected so as to cause all smoke alarms to sound a distinctive alarm signal upon actuation of any single smoke alarm. Such alarm signal shall be audible throughout the facility at a minimal level of 15 db above ambient noise level. These devices need not be interconnected to any other fire alarm device, have a control panel, or be electronically supervised or provided with emergency power.
907.2.11.2.4 Smoke alarms. Smoke alarms shall be tested and maintained in accordance with the manufacturer’s instructions. Smoke alarms that no longer function shall be replaced.
907.2.11.2.5 Existing Group R occupancies. See the California Residential Code for existing Group R-3 occupancies or Chapter 11 of the California Fire Code for all other existing Group R occupancies.
907.2.11.2.6 Group R-4. A manual fire alarm system that activates the occupant notification system in accordance with Section 907.5 shall be installed in Group R-4 occupancies housing nonambulatory clients.
907.2.11.3 Installation near cooking appliances. See Section 907.2.11.8.
907.2.11.4 Installation near bathrooms. See Section 907.2.11.8.
CRC § 5.2 High relevance — show source text
R335.5.2 Smoke alarms in Groups R-3.1 occupancies. Smoke alarms shall be installed where required in Section R314. In addition to the provisions set forth in Section R314 the following shall apply: 1. Smoke alarms shall be provided throughout the habitable areas of the dwelling unit except kitchens. 2. Facilities housing a bedridden client: 2.1. Smoke alarms shall receive their primary power from the building wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. 2.2. Smoke alarms shall be electrically interconnected so as to cause all smoke alarms to sound a distinctive alarm signal upon actuation of any single smoke alarm. Such alarm signal shall be audible throughout the facility at a minimal level of 15 db above ambient noise level. These devices need not be interconnected to any other fire alarm device, have a control panel, or be electrically supervised or provided with emergency power.
R335.5.2.1 Audible alarm signal. The audible signal shall be the standard fire alarm evacuation signal, ANSI S3.41 Audible Emer- gency Evacuation Signal, “three pulse temporal pattern,” as described in NFPA 72.
R335.5.2.2 Hearing impaired. See Section 907.5.2.3 of the California Building Code.
R335.5.2.3 Visible alarms. Visible alarm notification appliances shall be provided in accordance with Sections 907.5.2.3.1 through 907.5.2.3.5 of the California Building Codes.
Exceptions: 1. Visible alarm notification appliances are not required in alterations, except where an existing fire alarm system is upgraded or replaced, or a new fire alarm system is installed. 2. Visible alarm notification appliances shall not be required in enclosed exit stairways, exterior exit stairs and exterior exit ramps. 3. Visible alarm notification appliances shall not be required in elevator cars.
R335.5.2.4 Group R-3.1. Protective social care facilities which house persons who are hearing impaired, shall be provided with notification appliances for the hearing impaired installed in accordance with NFPA 72 and which shall activated upon initiation of the fire alarm system or the smoke alarms.
Exception: The use of the existing evacuation signaling scheme shall be permitted where approved by the enforcing agency.
R335.6 Means of egress provisions.
R335.6.1 General. In addition to the general means of egress requirements of Chapter 10 of the California Building Code, this section shall apply to Group R-3.1 occupancies.
R335.6.2 Number of exits.
3-80 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
BUILDING PLANNING
R335.6.2.1. Group R-3.1 occupancies shall have a minimum of two exits.
R335.6.3 Egress arrangements.
R335.6.3.1. Egress through adjoining dwelling units shall not be permitted.
CRC § 1103.7.9.10 High relevance — show source text
1103.7.9.10 Elevator recall smoke detection. Smoke detection for emergency operation of elevators shall be provided in accor- dance with Section 907.3.3.
1103.8 Single- and multiple-station smoke alarms. Single- and multiple-station smoke alarms shall be installed in existing Group I1 and R occupancies in accordance with Sections 1103.8.1 through 1103.8.3.
1103.8.1 Where required. Existing Group I-1 and R occupancies shall be provided with single-station smoke alarms in accordance with Section 907.2.11. Interconnection and power sources shall be in accordance with Sections 1103.8.2 and 1103.8.3, respectively.
Exceptions:
- Where the code that was in effect at the time of construction required smoke alarms and smoke alarms complying with those requirements are already provided.
- Where smoke alarms have been installed in occupancies and dwellings that were not required to have them at the time of construction, additional smoke alarms shall not be required provided that the existing smoke alarms comply with requirements that were in effect at the time of installation.
- Where smoke detectors connected to a fire alarm system have been installed as a substitute for smoke alarms.
1103.8.2 Interconnection. Where more than one smoke alarm is required to be installed within an individual dwelling or sleeping unit, the smoke alarms shall be interconnected in such a manner that the activation of one alarm will activate all of the alarms in the individual unit. Physical interconnection of smoke alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm. The alarm shall be clearly audible in all bedrooms over background noise levels with all intervening doors closed.
Exceptions:
- Interconnection is not required in buildings that are not undergoing alterations, repairs or construction of any kind.
- Smoke alarms in existing areas are not required to be interconnected where alterations or repairs do not result in the removal of interior wall or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available that could provide access for interconnection without the removal of interior finishes. 3. Smoke alarms are not required to be interconnected where repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addi- tion of a porch or deck. 4. Smoke alarms are not required to be interconnected when work is limited to the installation, alteration or repairs of plumbing or mechanical systems or the installation, alteration or repair of electrical systems which do not result in the removal of interior wall or ceiling finishes exposing the structure.
1103.8.3 Power source. Single-station smoke alarms shall receive their primary power from the building wiring provided that such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exceptions:
- Smoke alarms are permitted to be solely battery operated in existing buildings where construction is not taking place.
- Smoke alarms are permitted to be solely battery operated in buildings that are not served from a commercial power
source.
CRC § 907.2.11.6 High relevance — show source text
907.2.11.6 Power source. In new construction, and in newly classified Group R-3.1 occupancies, required smoke alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery back-up shall be connected to an emergency electrical system in accordance with Section 1203. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exception: Smoke alarms are not required to be equipped with battery backup where they are connected to an emergency electrical system that complies with Section 603.
907.2.11.7 Smoke detection system. Smoke detectors listed in accordance with UL 268 and provided as part of the building fire alarm system shall be an acceptable alternative to single- and multiple-station smoke alarms and shall comply with the following:
- The fire alarm system shall comply with all applicable requirements in Section 907.
- Activation of a smoke detector in a dwelling unit or sleeping unit shall initiate alarm notification in the dwelling unit or sleeping unit in accordance with Section 907.5.2.
- Activation of a smoke detector in a dwelling unit or sleeping unit shall not activate alarm notification appliances outside of the dwelling unit or sleeping unit, provided that a supervisory signal is generated and monitored in accordance with Section 907.6.6.
907.2.11.8 Specific location requirements.
Extract from NFPA 72 Section 29.11.3.4 Specific Location Requirements*.
This extract has been provided by NFPA for the Office of the State Fire Marshal adoption by reference as follows:
29.11.3.4 Specific location requirements. The installation of smoke alarms and smoke detectors shall comply with the follow- ing requirements:
(1) Smoke alarms and smoke detectors shall not be located where ambient conditions, including humidity and temperature, are outside the limits specified by the manufacturer's published instructions.
(2) Smoke alarms and smoke detectors shall not be located within unfinished attics or garages or in other spaces where temperatures can fall below 40ºF (4ºC) or exceed 100ºF (38ºC).
(3) Where the mounting surface could become considerably warmer or cooler than the room, such as a poorly insulated ceil- ing below an unfinished attic or an exterior wall, smoke alarms and smoke detectors shall be mounted on an inside wall.
(4) Smoke alarms and smoke detectors shall not be installed within an area of exclusion determined by a 10-foot (3.0 m) radial distance along a horizontal flow path from a stationary or fixed cooking appliance, unless listed for installation in close proximity to cooking appliances. Smoke alarms and smoke detectors installed between 10 feet (3.0 m) and 20 feet (6.1 m) along a horizontal flow path from a stationary or fixed appliance shall be equipped with an alarm-silencing means or use photoelectric detection.
(5) Smoke alarms or smoke detectors that use photoelectric detection shall be permitted for installation at a radial distance greater than 6 feet (1.8 m) from any stationary or fixed cooking appliance when both of the following conditions are met: (a) The kitchen or cooking area and adjacent spaces have no clear partitions or headers.
9-46 2025 CALIFORNIA FIRE CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FIRE PROTECTION AND LIFE SAFETY SYSTEMS
CRC § 907.2.11.2 High relevance — show source text
[F] 907.2.11.2 Groups R-2, R-2.1, R-2.2, R-3, R-3.1, R-4 and R-4.1 . Single- or multiple-station smoke alarms shall be installed and maintained in Groups R-2, R-2.1, R-2.2, R-3, R-3.1 and R-4 regardless of occupant load at all of the following locations:
- On the ceiling or wall outside of each separate sleeping area in the immediate vicinity of bedrooms.
- In each room used for sleeping purposes.
- In each story within a dwelling unit, including basements but not including crawl spaces and uninhabitable attics. In dwellings or dwelling units with split levels and without an intervening door between the adjacent levels, a smoke alarm installed on the upper level shall suffice for the adjacent lower level provided that the lower level is less than one full story below the upper level. 4. In a Group R-3.1 occupancies, in addition to the above, smoke alarms shall be provided throughout the habitable areas of the dwelling unit except kitchens. See Section 907.2.11.8 for specific location requirements. 907.2.11.2.1 Licensed Group R-2.1 occupancies. Licensed Group R-2.1 occupancies housing more than six nonambulatory, elderly clients shall be provided with an approved manual and automatic fire alarm system. Exceptions: Buildings housing nonambulatory clients on the first story only and which are protected throughout by the following: 1. An approved and supervised automatic sprinkler system, as specified in the California Fire Code Sections 903.3.1.1 or 903.3.1.2, which upon activation will initiate the fire alarm system to notify all occupants.
2025 CALIFORNIA BUILDING CODE 9-31
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FIRE PROTECTION AND LIFE SAFETY SYSTEMS
2. A manual fire alarm system. 3. Smoke alarms required by the California Fire Code Section 907.2.10.
907.2.11.2.1.1 Smoke alarms. Single- and multiple-station smoke alarms shall be installed in accordance with California Fire Code Section 907.2.11.
907.2.11.2.2 Group I-4 occupancies. Large family day-care homes shall be equipped with State Fire Marshal approved and listed single station residential type smoke alarms.
907.2.11.2.3 Group R-3.1. In all facilities housing a bedridden client, smoke alarms shall receive their primary power from the build- ing wiring when such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms shall be electrically interconnected so as to cause all smoke alarms to sound a distinctive alarm signal upon actuation of any single smoke alarm. Such alarm signal shall be audible throughout the facility at a minimal level of 15 dB above ambient noise level. These devices need not be interconnected to any other fire alarm device, have a control unit, or be electrically supervised or provided with emer-
gency power.
CRC § 907.2.11.2.6 High relevance — show source text
907.2.11.2.6 Group R-4. A manual fire alarm system that activates the occupant notification system in accordance with Section 907.5 shall be installed in Group R-4 occupancies housing nonambulatory clients.
[F] 907.2.11.3 Installation near cooking appliances. See Section 907.2.11.8.
[F] 907.2.11.4 Installation near bathrooms. See Section 907.2.11.8.
[F] 907.2.11.5 Interconnection. Where more than one smoke alarm is required to be installed within an individual dwelling unit or sleeping unit in Group R occupancies, the smoke alarms shall be interconnected in such a manner that the activation of one alarm will activate all of the alarms in the individual unit. Physical interconnection of smoke alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm. The alarm shall be clearly audible in all bedrooms over background noise levels with all intervening doors closed.
[F] 907.2.11.6 Power source. In new construction, and in newly classified Group R-3.1 occupancies, required smoke alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source and shall be equipped with a battery backup. Smoke alarms with integral strobes that are not equipped with battery backup shall be connected to an emergency electrical system in accordance with Section 2702. Smoke alarms shall emit a signal when the batteries are low. Wiring shall be permanent and without a disconnecting switch other than as required for overcurrent protection.
Exception: Smoke alarms are not required to be equipped with battery backup where they are connected to an emergency electrical system that complies with Section 2702.
[F] 907.2.11.7 Smoke detection system. Smoke detectors listed in accordance with UL 268 and provided as part of the building fire alarm system shall be an acceptable alternative to single- and multiple-station smoke alarms and shall comply with the following:
- The fire alarm system shall comply with all applicable requirements in Section 907.
- Activation of a smoke detector in a dwelling unit or sleeping unit shall initiate alarm notification in the dwelling unit or sleeping unit in accordance with Section 907.5.2.
- Activation of a smoke detector in a dwelling unit or sleeping unit shall not activate alarm notification appliances outside of the dwelling unit or sleeping unit, provided that a supervisory signal is generated and monitored in accordance with Section 907.6.6.
907.2.11.8 Specific location requirements.
Extract from NFPA 72 Section 29.11.3.4 Specific Location Requirements*.
This extract has been provided by NFPA for the Office of the State Fire Marshal adoption by reference as follows:
29.11.3.4 Specific location requirements. The installation of smoke alarms and smoke detectors shall comply with the following requirements: (1) Smoke alarms and smoke detectors shall not be located where ambient conditions, including humidity and temperature, are outside the limits specified by the manufacturer's published instructions. (2) Smoke alarms and smoke detectors shall not be located within unfinished attics or garages or in other spaces where temperatures can fall below 40ºF (4ºC) or exceed 100ºF (38ºC). (3) Where the mounting surface could become considerably warmer or cooler than the room, such as a poorly insulated ceil- _ing below an unfinished attic or an exterior wall, smoke alarms and smoke detectors shall be mounted on an inside wall.
Frequently asked questions
Do smoke alarms have to be interconnected in an existing home?
Interconnection is required where more than one alarm is required, but CRC provides exceptions for existing buildings when no qualifying work is being done or where finishes are not opened up (see § R310.4 Exceptions) .
Can I use wireless alarms to meet interconnection?
Yes — if the wireless alarm system is listed for that purpose and all alarms sound upon activation of one device; installation still must follow the device listing and manufacturer instructions (§ R310.4, § R310.1.2) .
Are battery‑only alarms ever allowed?
Yes — in specific existing building situations (no construction, buildings without commercial power, or limited repair/alteration scenarios listed in § R310.6 Exceptions) battery‑only alarms are permitted; in new construction building‑wired primary power with battery backup is required (§ R310.6) .
What listing standard must smoke alarms meet?
Smoke alarms must be listed and labeled to UL 217; combination smoke/CO alarms must meet UL 217 and UL 2034 as applicable (§ R310.1.1) .
Does “installed per manufacturer” ever trump code location rules?
No — manufacturer/listing instructions govern proper installation technique, but code‑required locations (e.g., outside sleeping areas, in each sleeping room, each story) must still be met; use an alarm whose listing permits the required mounting location and spacing (§ R310.1.2, § R310.3) .
More in California Residential Code
Ask about the CRC
Get cited, plain-English answers on the California Residential Code for your project — any code section, any scenario.
Start Free Trial