Smoke & Carbon Monoxide Alarm Requirements in California

The basic rule

State law requires smoke alarms “in each dwelling intended for human occupancy,” installed following the manufacturer’s instructions and “approved and listed by the State Fire Marshal” (H&S Code §13113.7).

Carbon monoxide (CO) alarms are required in a home that has “a fossil fuel burning heater or appliance, fireplace, or an attached garage” (H&S Code §17926). For single-family homes, that deadline passed on July 1, 2011. A gas furnace or gas water heater is a common example. The building code words the garage trigger as “an attached garage with an opening that communicates with the dwelling unit” (CRC R311.2.1).

Where the alarms go

The California Residential Code sets the locations (2025 CRC, R310.3 and R311.3).

Smoke alarms:

In each bedroom.
Outside each sleeping area, near the bedrooms.
On every story, including basements and habitable attics (not crawl spaces or uninhabitable attics).
At least 3 feet from the door of a bathroom with a tub or shower, where that’s possible.

The code also keeps smoke alarms away from cooking appliances, heating and cooling supply registers and ceiling fans (R310.3.3), so placement in a kitchen or a great room takes some care.

CO alarms:

Outside each sleeping area, near the bedrooms.
On every occupiable level, including basements.
Inside a bedroom that has a fuel-burning appliance in it or in its attached bathroom.

A combination smoke and CO alarm can take the place of either one (R310.5, R311.4).

What a remodel or addition triggers

This is the rule that catches homeowners by surprise. Under the building code, “Where alterations, repairs or additions requiring a permit occur, the individual dwelling unit shall be equipped with smoke alarms located as required for new dwellings” (CRC R310.2.2). In other words, the whole home, not just the room you’re working on (with the exceptions for battery power below).

State law adds a sign-off rule. For a permit for “alterations, repairs, or additions exceeding one thousand dollars ($1,000),” the building department “shall not sign off on the completion of work” until the alarms are State Fire Marshal listed (§13113.7(a)(2)). If the state updates its CO alarm standards, an owner who installed CO alarms as the law required doesn’t have to replace them until applying for a permit for work over $1,000 (§17926.2).

For CO alarms, the code requires new ones when you build an addition, or when you add a fuel-burning heater, appliance or fireplace to a home that didn’t need CO alarms before, unless the work is limited to outside surfaces, plumbing, or mechanical work that isn’t fuel fired (CRC R311.2.2). Ask your building department what it will check at the final inspection.

Hardwired or battery?

New work calls for alarms wired to the house power with a battery backup, and, where more than one is required, interconnected so that one sounding sets them all off (CRC R310.4, R310.6, R311.5, R311.6). Existing areas get some relief. Battery-only smoke alarms without interconnection are allowed when (R310.4, R310.6):

the work doesn’t remove interior wall or ceiling finishes and expose the framing, unless an attic, crawl space or basement gives access for wiring;
the work is limited to the outside of the house, such as a new roof, siding, windows, doors, a porch or a deck; or
the work is limited to plumbing, mechanical or electrical work that doesn’t open the walls or ceilings.

So a kitchen or bathroom remodel that opens walls usually means hardwired, interconnected smoke alarms in that area, while a reroof usually doesn’t. CO alarms required because of an addition or a new fuel-burning appliance may be battery powered (R311.6). Your building department makes the call for your project.

A smoke alarm that runs only on a battery must have “a nonreplaceable, nonremovable battery that is capable of powering the smoke alarm for at least 10 years” to be listed in California (H&S Code §13114). Listed alarms also show their date of manufacture and have a place to write the installation date.

Selling a house

“[E]very single-family dwelling … which is sold shall have an operable smoke alarm,” and the seller gives the buyer a written statement that the house complies (H&S Code §13113.8). Check the CO alarms at the same time, since §17926 applies to existing homes too.

Renting a house

Landlords are responsible for testing and maintaining smoke alarms in a rented single-family home, and at the start of a new tenancy “the owner shall ensure that smoke alarms are operable” (§13113.7(d)). CO alarms must be “operable at the time that the tenant takes possession” (H&S Code §17926.1). Tenants are expected to report an alarm that stops working.

Before your project

Ask your contractor whether the permit will trigger alarm upgrades and whether they’re in the estimate, since adding hardwired alarms is easiest while walls and ceilings are open. Our guide on building permits covers when a permit is needed, and our remodeling page covers how a remodel usually goes.

Smoke and carbon monoxide alarms: what California requires