The First Alert P1210E 10 years battery photoelectric smoke alarm, slim profile with escape light helps protect your home by providing up to a decade of uninterrupted monitoring. This low-profile smoke alarm uses an ultra-reliable photoelectric sensor to detect smoke from slow-burning, smoldering fires. Half as thick as a standard alarm, this detector has a slim, contemporary design that mounts unobtrusively on a wall or ceiling. A built-in 10 years lithium-ion battery provides continuous power, with no need to ever worry about changing the battery over the lifetime of the smoke detector.