Whenever a sale (or exchange) of a single family dwelling occurs, the seller must provide the buyer with a written statement representing that the property is in compliance with California law regarding smoke detectors. Some local ordinances impose more stringent smoke detector requirements than state law. Therefore, local city or county building or public safety departments should be consulted regarding smoke detector requirements.

The State Building Code mandates that all existing dwelling units have a smoke detector installed in a central location outside each sleeping area. In a two-story home with bedrooms on both floors, at least two smoke detectors would be required.

New construction, or any additions, alterations or repairs exceeding $1,000 and for which a permit is required, must include a smoke detector installed in each bedroom and also at a point centrally located in a corridor or area outside of the bedroom(s). This standard applies for the addition of one or more bedrooms, no matter what the cost.
In new home construction, the smoke detector must be hard-wired, with a battery backup. In existing dwellings, the detector may be battery operated.

(Cal. Health & Safety § 13113.8; Cal. Building Code § 1210; State Fire Marshall Regulations 740 et. seq.)