Effective January 1, 2013 all residential multi-unit dwellings; and
Since July 1, 2011 all single family dwellings must have carbon monoxide devices installed. 

New California State Law Requires Carbon Monoxide Device(s)

Property owners should be aware that a new California State Law makes it mandatory for all dwelling units intended for human occupancy (Both owner occupied & rental) are required to have carbon monoxide device(s), approved and listed by the State Fire Marshal, in each existing dwelling unit that is equipped with fossil fuel burning appliances, fireplace, or has an attached garage.  Property owners are required to comply with this new State law as follows:

With respect to the number and placement of the carbon monoxide device(s), the owner shall install the device(s) in a manner consistent with building standards for new construction relevant to the type of occupancy and/or per the manufactures installation instructions. (See links below)

For Additional Information