Smoke Alarm W/Battery Back-Up AC/DC 9120B

120V (volt) AC (alternating current) wired-in smoke alarm with 9V battery back-up. Ionization sensor detects fast flaming fires. Battery compartment swings out, making battery installation easier and faster. Universal mounting bracket centers on any size electrical box up to 4 In. octagonal. Locking feature deters removal of battery. Battery life varies according to use and application. Silence button quiets alarm while occupants respond. Limited 10-year warranty. UL (Underwriter's Laboratories) listed.