One smoke alarm isn't enough! You should have at least one smoke alarm in every bedroom and in the hallway outside each bedroom. A typical 3 bedroom home would need at least 4 properly installed smoke alarms to provide a reasonable amount of protection for your family.
Smoke rises, so the best place to install an alarm is on the ceiling or high on an inside wall approximately 6-8 inches below the ceiling. Anytime your smoke alarm goes off, check your home thoroughly. If you see or smell smoke, immediately get out of your home and call 911. If the detector is chirping, replace the battery as soon as possible. Without a working battery, a smoke detector can't do its job and the risk of dying in a fire increases greatly.