California smoke and CO alarm rules, and exactly where each one goes

It chirps at 3 a.m., of course, from the hallway ceiling you can't reach without a chair. Before you climb up, it helps to know what California actually asks of your alarms, because the answer decides whether you need a battery, a new alarm or an electrician. The law fits on one page. Where each alarm goes is the part that trips people up.

#What California requires, in one table

The duties sit in the Health and Safety Code. The placement detail sits in the building code, which since January 1, 2026 is the 2025 California Residential Code; its smoke alarm section is now R310 and its carbon monoxide section R311, so a handout citing other section numbers is likely quoting an earlier edition. San Francisco layers its own Housing Code rules on top for rentals.

#Which rooms need which alarm

Start with coverage. Walk each floor with this list and tick what's already there; the list remembers your progress on this device, so it's fine to finish over a weekend.

#Exactly where: ceilings, kitchens and bathroom doors

The rooms are the easy part. Distances are where alarms land in the wrong place, right outside a steamy bathroom or over the stove, and then get disabled because they won't stop going off. Tap the plan for the measurements that matter. On an old lath-and-plaster ceiling, mount with the care the plaster guide describes.

Alarms only warn. The Fire Department's carbon monoxide page asks for fuel-burning heating equipment and chimneys to be inspected by a professional every year before the cold sets in, vents kept clear, cars never left idling indoors and generators run outside, away from windows and doors. Anyone who burns wood will find the burn-day rules in the fireplace season guide.

#The 10-year battery law, and what it doesn't require

Since July 1, 2014, a smoke alarm that runs only on batteries can be listed for sale in California only if its battery is sealed in, can't be removed and lasts at least 10 years (Health and Safety Code 13114). Since January 1, 2015, every listed alarm shows its manufacture date, has a spot to write the installation date and has a hush feature. The law decides what stores can sell. It never ordered anyone to pull down a working alarm.

• Heard this?The 10-year law made my working alarms illegal.Tap for the factsWhat's trueIt controls which alarms can be listed and sold. For rentals, the statute says existing alarms need not be replaced unless they don't work. Separately, the U.S. Fire Administration says to replace any smoke alarm 10 years after its manufacture date.
• Heard this?Hardwired alarms last as long as the wiring.Tap for the factsWhat's trueThey wear out like any other. The Fire Administration's schedule for a hardwired alarm: test it monthly, change the backup battery yearly, replace the unit every 10 years.
• Heard this?CO alarms need sealed 10-year batteries too.Tap for the factsWhat's trueNot on their own. The State Fire Marshal says it isn't aware of a 10-year battery requirement for CO-only alarms. A battery-powered combination smoke and CO alarm does need the sealed battery and an end-of-life warning to be listed.
• Heard this?Taking the battery out is the fix for cooking alarms.Tap for the factsWhat's trueThe Fire Administration says never remove it. Open a window, press hush and wave a towel; if it keeps happening, move the alarm several feet farther from the kitchen.
• Heard this?No gas in my unit, so no CO alarm.Tap for the factsWhat's trueThe State Fire Marshal's FAQ says otherwise for an apartment in a building with an attached garage or gas heat in a common hallway, because CO can reach the unit through openings and ventilation.

#Why it's chirping, and what to do about it

#Landlords, tenants and the day you sell

For a rental, Section 13113.7 puts testing and maintenance on the owner. Smoke alarms must work when a new tenancy begins; the tenant's job is to tell the owner when one doesn't, and an owner who was never told isn't in violation. To install, repair or test alarms, an owner may enter with reasonable written notice, presumed to be 24 hours, during normal business hours unless there's an emergency. Section 17926.1 sets up the same split for carbon monoxide devices.

Selling a single-family home, which the statute defines to include a one- or two-unit building, takes an operable smoke alarm and a written statement to the buyer that you comply (Section 13113.8). Remodeling raises the bar: on permitted work over $1,000, the inspector won't sign off until every required alarm is State Fire Marshal listed. The selling guide and the permit guide cover the rest of each process.

#Sunday, November 1, 2026: test day

Clocks fall back at 2 a.m. on Sunday, November 1, 2026, according to NIST. The Fire Department ties its yearly battery change to the clock change, and a weekend on the calendar beats a chirp at 3 a.m. Twenty minutes covers most homes.

1. Press and hold the test button on every smoke and CO alarm. The Fire Department suggests doing it monthly.
2. Read the date on the back of each one, and replace any that are 10 years past it.
3. Change the battery in alarms that take one; a sealed 10-year alarm gets replaced whole.
4. Vacuum the vents. Dust and cobwebs dull the sensor, and the Fire Department says to do it at least once a year.
5. Look for alarms someone painted over. The Fire Department says never to paint one; replace it.
6. Agree on a meeting spot outside and practice getting there. The Fire Department recommends family fire drills.