California law requires working smoke alarms in every bedroom, outside each sleeping area, and on every floor of a home, plus a carbon monoxide alarm on each level and near sleeping areas in any house with a fuel-burning appliance, fireplace, or attached garage. Since 2014 most battery-only smoke alarms sold here must have a sealed 10-year battery. Sellers also have duties at the point of sale.
What the smoke alarm rules actually say
California’s smoke alarm placement standard comes from the State Fire Marshal regulations and the California Residential Code, and it has tightened over the years. For a typical single-family home, the requirement is straightforward once you break it into three rules:
- Inside every bedroom. Each room used for sleeping needs its own smoke alarm.
- Outside each separate sleeping area. This means the hallway or space immediately serving the bedrooms – so a home with bedrooms in two separate wings needs an alarm outside each grouping.
- On every level, including basements. A two-story house with no bedrooms downstairs still needs an alarm on the lower floor. Habitable attics and split-level steps factor in too.
Placement details matter as much as count. Alarms should be on the ceiling or high on the wall, kept away from the immediate path of kitchen cooking and bathroom steam (both trigger nuisance alarms), and not tucked into a corner where air doesn’t circulate. In homes built or substantially remodeled under newer code, smoke alarms are hardwired with a battery backup and interconnected, so when one sounds they all sound. Older homes are often battery-only, which is legal for existing construction but raises the bar on the battery rule below.
The 10-year sealed battery law
This is the rule that trips up the most homeowners. Under California law (SB 745), most solely battery-powered smoke alarms manufactured on or after July 1, 2014 and sold in the state must contain a non-replaceable, non-removable battery capable of powering the alarm for at least 10 years. The goal was to stamp out the classic failure mode: a resident pulls a chirping 9-volt battery at 2 a.m. and never replaces it.
A few practical takeaways flow from this:
- If you’re replacing a dead battery-only alarm, the new unit needs to be a sealed 10-year model. You generally can’t buy a compliant swap-the-battery unit anymore.
- Hardwired alarms are exempt from the sealed-battery requirement because they draw house power; they still use a backup battery you can change.
- Every smoke alarm has a manufacture date stamped on the back. Smoke alarms have a service life – 10 years from that date – after which the sensor degrades and the whole unit should be replaced, sealed battery or not. An alarm with a 2012 date stamp is past due regardless of whether it still beeps when tested.
Carbon monoxide alarm requirements
The Carbon Monoxide Poisoning Prevention Act requires CO alarms in every “dwelling unit intended for human occupancy” that has any of three things: a fuel-burning appliance (gas furnace, gas water heater, gas range or oven, gas dryer, wood or gas fireplace), a fireplace, or an attached garage. Carbon monoxide is colorless and odorless, and a running engine or a cracked heat exchanger can fill a house before anyone notices – which is exactly why the attached-garage trigger exists.
Placement for CO alarms is its own standard:
- Outside each separate sleeping area, in the immediate vicinity of the bedrooms, so it can wake people who are asleep.
- On every level of the home, including basements.
An all-electric home with no fireplace and no attached garage technically falls outside the CO requirement – but adding an alarm anyway is cheap insurance, especially since a portable generator or an attached neighbor’s unit can still introduce CO. Combination smoke/CO alarms are allowed and are a tidy way to satisfy both rules at one location, as long as the combined unit is listed and placed correctly for each function.
What a home inspector notes about detectors
A general home inspection is a visual, non-invasive assessment, and smoke and CO alarms are part of the walkthrough. Here’s what we actually document and what falls outside our scope. We note whether alarms are present and located in the bedrooms, hallways, and on each level the code contemplates, and whether a CO alarm exists where fuel appliances or an attached garage make one mandatory. We note visibly missing, obviously expired (by date stamp), or improperly placed units – for example, a smoke alarm mounted directly over a stove, or no CO alarm in a house with a gas furnace.
What an inspection is not: it’s not a code-compliance certification, and pressing the test button only confirms the horn and battery work, not that the sensor still detects smoke or CO accurately. We can’t see inside a sealed unit, and we don’t issue the kind of pass/fail certificate some jurisdictions require at sale. Think of the inspection as a thorough flag-the-gaps review, not a legal sign-off. If you want the full picture of what’s covered and what isn’t, our San Diego home inspection checklist walks through the broader scope, and our page on inspection limitations explains the line between visual review and specialized testing.
Seller obligations at the point of sale
California ties detector compliance to the transfer of residential property. The seller of a dwelling is responsible for ensuring the home is equipped with the required smoke and carbon monoxide alarms before the sale closes. In practice this shows up two ways. First, on the Transfer Disclosure Statement (the TDS, required for sellers of one-to-four residential units under Civil Code 1102), the seller discloses whether the property has smoke and CO alarms. Second, purchase contracts routinely make the seller warrant that compliant alarms will be in place at close of escrow.
A couple of points sellers get wrong:
- “As-is” does not erase this. Selling a home as-is limits some repair expectations, but it does not remove the statutory duty to disclose known material facts or the detector requirements that attach to the transfer.
- It’s inexpensive to fix. Bringing a home into compliance usually means buying a handful of sealed 10-year smoke alarms and a CO alarm or two – far cheaper than a renegotiation triggered by a buyer’s inspection finding missing alarms.
If you’re listing, handling detectors before photos is the smart move; our guidance on pre-listing inspections for San Diego sellers covers the small fixes that keep a deal clean. Buyers should treat missing or expired alarms as an easy ask, and our buyer’s inspection service flags them as a matter of course.
The bottom line
Smoke alarms belong in every bedroom, outside each sleeping area, and on every floor; CO alarms belong on each level and near bedrooms whenever the home has a fuel appliance, fireplace, or attached garage; and most battery-only smoke alarms in California must be sealed 10-year units. These are among the cheapest safety upgrades a homeowner can make and the most avoidable findings on an inspection report. To schedule an inspection or ask how detector requirements apply to a specific San Diego County property, reach The Real Estate Inspection Company at (619) 752-4399. For legal specifics on disclosure duties, confirm the current statute and consult your agent or attorney.
