A smoke detector, also called a smoke alarm, has a limited life span. Fire safety experts say any smoke detector 10 years old or older should be replaced right away. This rule applies to all types of smoke detectors, regardless of whether they are hardwired or battery powered.
Smoke detectors come in two basic types. The ionization type is most responsive to flaming fires while the photoelectric type works best at detecting smoldering fires. For comprehensive protection, a homeowner should install both types of detectors. The best location is in the middle of the ceiling or high on a wall but at least 4 inches below the ceiling. Over the span of a decade, however, both types become less sensitive to smoke and fire because of factors such as dust buildup in the sensing chamber and component failure. Old detectors cannot be renewed; replacement is the only option.
Test your smoke detectors monthly to make sure they are working. Most models have a test button you press to find out if the alarm sounds. Blow any dust or cobwebs away from the unit when testing. For detectors with replaceable batteries, install new batteries annually until the detector itself is due for replacement. For models powered by a 10-year, long-life lithium battery, replace the entire unit after 10 years. If you have hardwired units, annually replace any backup battery and replace the entire unit after 10 years.