Most homes require smoke detectors, but where do they go? The California Fire Marshall is in charge of this regulation.   The CalFire site states the following, which applies to most dwellings :

Placement
Install smoke alarms in every bedroom, in the hallways leading to the bedrooms, and on each level of your home, including the basement. Smoke alarms should be mounted on the ceiling 4” from the wall; wall mounts should be 4-12” from the ceiling. Do not install near draft areas (windows, vents.). Call your local fire department if you are unsure about placement.

For more information:

http://www.ca.gov/HealthSafety/LawsAndRegs.html

 http://www.leginfo.ca.gov/cgi-bin/calawquery?codesection=hsc