The Kidde P9050 is a battery operated smoke alarm, equipped with a photoelectric sensor, designed to alert you and your family to the dangers of smoke and fire. The P9050 includes a 9V battery, providing you protection even during a power failure. This unit is UL Listed and offers a 10-year limited warranty. This alarm uses photoelectric sensing technology. Photoelectric sensing alarms may detect visible particles (associated with smoldering fires) sooner than ionization alarms. Ionization sensing alarms may detect invisible fire particles (associated with flaming fires) sooner that photoelectric alarms.