Smoke detectors are an inexpensive early warning device that saves lives.
Smoke detectors should be placed on every level of the home, including the basement. They should be placed near bedrooms and other living spaces but not in a kitchen or directly outside a bathroom where they may create nuisance alarms.
All smoke detectors are only as good as the degree to which they are maintained. Batteries should be replaced at least once a year. Twice a year is better. Periodically vacuum the unit to clear it of dust and cob-webs. Smoke detectors have a good track record for saving lives when properly placed and maintained in the home.
Under the best of circumstances you have approximately 1-2 minutes to safely exit your home when you hear the smoke detector alarm.