The placement of smoke detectors is very important. Sleeping areas need the most protection. One detector in a short hallway outside the bedroom area is usually adequate. Hallways longer than 30 feet should have 1 at each end. For maximum protection, install a detector in each bedroom.
Be sure to keep the detector away from fireplaces and wood stoves to avoid false alarms. Place smoke detectors at the top of each stairwell and at the end of each long hallway. Smoke rises easily through stairwells. If you should put a smoke detector in your kitchen, be sure to keep it away from cooking fumes or smoking areas.
Proper mounting of a smoke detector also is important. You can mount many detectors by yourself, but those connected to your household wiring should have their own separate circuit and be installed by a professional electrician. If you mount your detector on the ceiling, be sure to keep it at least 18 inches away from dead air space near walls and corners. If you mount it on the wall, place it 6 to 12 inches below the ceiling and away from corners. Keep them high because smoke rises.
Never place them any closer than 3 feet from an air register that might circulate smoke. Don't place them near doorways or windows where drafts could impair the detector operation. Don't place them on an uninsulated exterior wall or ceiling. Temperature extremes can affect the batteries.