You need to have smoke detectors in each sleeping room, in the hallway outside of sleeping rooms and on each floor level of your home. The most common place to put a smoke detector is on the ceiling of the room. The detector should be mounted no closer than 12 inches from the side wall or if mounted on the wall, no closer than 12 inches from the ceiling. Make sure not to place the detector outside of bathroom doors, in kitchens, and other areas that produce vapors that might lead to accidental detector activations.
There are two basic types of smoke detectors - ionic and photoelectric. Both types of detectors work well to detect fires where there are open flames. Tests have shown that the photoelectric detectors are better in detecting smoldering fires, the type of fire most common in homes.
All new homes are required to have smoke detectors that run off of the normal household electrical circuits with battery backup. Older homes, built before smoke detectors were required are often supplied with battery-operated smoke detectors only. Hard wired detectors that run off of a home's normal electricity can be installed or retrofitted into existing homes.