Smoke detectors save lives, period. You should have a smoke detector on each floor
and a smoke detectors near sleeping areas at minimum. If your smoke detectors are battery
powered, check the batteries once a month and change them once a year.
If your smoke alarm is nearing 7 years old or more, it's too old to be reliable
and you should replace it with a new smoke alarm.
Smoke alarms use two main technologies. Ionization and Photoelectric. Ionization smoke detectors are best at detecting fast flaming fires.
Photoelectric smoke alarms ares best at detecting smoky, smoldering fires.
Some interesting links:
Fire Safety Council
Ionization Smoke Detectors vs Photoelectric Smoke Alarms
