Beginning July 1, 2011, the Carbon Monoxide Poisoning Prevention Act brought by California Senate Bill – SB 183 now requires all single-family homes with an attached garage or a fossil fuel source to install carbon monoxide alarms by July 1, 2011. In Simi Valley almost every home I have been in, has a natural gas furnace in the house or attic and most homes have gas appliances in the kitchen. These gas appliances and the furnace trigger the installation of the carbon monoxide detectors.
The alarms are required to be installed outside of each sleeping area and at least one per floor of living space. The mounting height according to the National Fire Protection Association (NFPA 720), appears to not effect performance. I have read that density of carbon monoxide is similar to that of air at room temperature, and carbon monoxide generally mixes readily with air. Considering that the CO alarms come in a plug in style, battery operated or hard wire installation mounting height may not be an issue. However, some firemen I have spoke to recommend a lower installation height rather than up on the ceiling. You can buy a combination smoke alarm/carbon monoxide alarm, but plug in CO alarms are readily available and require no mounting hardware. Smoke alarms are still required, this new law does not change the smoke alarm requirements. For those who want to be extra cautious you can place a CO alarm in each bedroom.