The First Alert PR710 Slim Photoelectric Smoke Alarm with 10-Year Battery 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-year Li-Ion battery provides continuous power with no need to ever worry about changing the battery over the lifetime of the smoke detector.