The Kidde P12040 is a 120VAC powered photoelectric smoke alarm with 9V battery back up. This advanced smoke alarm has the ability to function as a stand-alone unit or in an interconnected system. The Kidde P12040 includes a test button, quick-connect power harness 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. Kidde strongly recommends that both ionization and photoelectric smoke alarms be installed to help insure maximum detection of the various types of fire that can occur within the home. The Kidde model P12040 is a 120VAC powered alarm that includes a 9V battery backup to provide continuous protection during a power failure and included a quick connect power harness to make installation simple.