For residential properties
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Updated: 04/14/2026

Referenced Codes
CRC Sections R310 and R311

State law requires all residential dwelling units to have smoke alarms. Carbon monoxide alarms are also required in certain spaces. These alarms save lives so keep them functioning properly. 

• Alarm models must be listed and approved by the California State Fire Marshal; the alarm packaging should have a CSFM Listing Seal.
• Alarms must be installed in accordance with the manufacturer’s instructions.
• Test your smoke alarms twice a year at minimum, monthly is better. Replace the alarms if they are more than 10 years old.

SMOKE ALARMS

Required locations

1. In each bedroom or sleeping area.
2. Outside of each sleeping area in the immediate vicinity of the bedrooms, such as the hallway that opens to bedrooms or sleeping areas.
3. On each story of the dwelling unit, including basements and habitable attics (but not in crawl spaces or uninhabitable attics).
4. In dwelling units with split levels and without an intervening door between the adjacent levels, a smoke alarm that is installed on the upper level will suffice for the adjacent lower level provided that the lower level is less than one full story below the upper level.
5. If a hallway that serves bedrooms opens to a room where the ceiling height of the room exceeds that of the hallway by 24 inches or more, then place a smoke alarm in both the higher ceiling room and in the hallway.
6. Within the room to which a sleeping loft is open, in the immediate vicinity of the sleeping loft.
7. Unless necessary to meet other requirements, install alarms not less than 3 feet from the door to a bathroom containing a tub or shower to avoid nuisance alarms. 

CARBON MONOXIDE ALARMs

Required locations

Carbon monoxide alarms are required in dwelling units where any of the following are found:

• A fireplace
• A fuel-fired appliance, such as a furnace, fireplace, water heater, clothes dryer, etc.
• An attached garage that has any kind of opening to the dwelling unit

If any of the above exist, then place a carbon monoxide alarm in these locations:

1. Outside each sleeping area in the immediate vicinity of the bedrooms.
2. On every occupiable level of the dwelling unit, including basements.
3. Within the bedroom if a fuel-burning appliance or fireplace is located within the bedroom or its attached bathroom.

When to hardwire and interconnect the alarms

If the alarms are hardwired and interconnected, then when one alarm goes off, so do all the others. This alerts everyone in all parts of the house before a fire gets too big in a more distant part of the house.

• During a fire, get out right away.
• For a carbon monoxide leak, first open windows and shut off appliances before leaving.
• Learn the difference in sounds between smoke and carbon monoxide alarms so you know the right response. 

REQUIREMENT: Where two or more smoke alarms or two or more carbon monoxide alarms are required, they shall be interconnected in such a manner that actuation of one shall cause actuation of all detectors in the dwelling unit. (CBC 907.2.11, CRC R314, CRC R315). Hardwiring — which means directly connecting to the dwelling unit’s electrical system — is required when there is a project that entails:

• new construction and alterations
• projects where building finishes are removed
• projects where an accessible attic for wiring is available

Hardwired alarms must have a backup battery installed. In the event of a power failure, the battery serves to keep the alarm operable. You must check and replace the batteries as they age. Hardwiring can only be performed by a licensed electrician.

Alarms are permitted to be solely battery-operated (not hardwired) under the following conditions: 

1. Where no construction is taking place.
2. In buildings not served by a commercial power source.
3. In existing areas of buildings undergoing alterations or repairs that do not result in the removal of interior wall or ceiling finishes, unless there is an attic, crawl space or basement available which could provide access for building wiring without the removal of interior finishes.
4. Where repairs or alterations are limited to exterior surfaces, such as roofing or siding, the addition or replacement of windows or doors, or the addition of a porch or deck.
5. Where work is limited to alterations or repairs of plumbing, mechanical or electrical systems which does not result in the removal of interior wall or ceiling finishes.
6. Note: The batteries installed in the alarms must be long-life (10 year) sealed type.

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