If you mount it on the wall, place it six to 12 inches below the ceiling and away from corners. Keep them high because smoke rises. Never place them any closer than three feet from an air register that might recirculate 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.
Maintenance Keeping smoke detectors in good condition is easy. Always follow the manufacturer's instructions. Be sure to replace the batteries every year or as needed. Most models will make a chirping, popping or beeping sound when the battery is losing its charge. When this sound is heard, install a fresh battery, preferably an alkaline type.