MOST fatal fires occur at night...it's true, most fatal fires happen when people are asleep. It is very important to have at least one smoke detector near the bedroom areas to wake you in case of fire. In homes that have more than one level, put at least one smoke detector on each level.
The absolute best protection is to have a smoke detector in every room, in corridors and hallways, and at the top of each stairway. There is no such thing as over careful when it pertains to the safety of you and your loved ones.
Having a smoke detector in the hall outside the bedrooms is very important, but if the bedroom doors are closed, a fire that is in the bedroom may not be detected quickly by the smoke detector, so additional detectors may be needed in the bedrooms as well.
Check the detectors periodically to make sure they are working properly. Change the batteries at least once a year. It is even better if you change the detectors when ' you change your clocks back and forward for DST (Daylight Savings Time).
Use only alkaline batteries, or batteries that are recommended by the manufacturer of the smoke detector. It is wise to keep a spare alkaline battery on hand for your detector.