The First Alert SC9120LBL alarm features a dual ionization smoke sensing chamber and an electrochemical carbon monoxide sensor, an 85Db horn and a ''silence'' feature. This alarm features a 10 year battery backup. The battery drawer is shipped pre locked so battery will not be discarded prematurely. Under normal conditions you should not have to replace the battery for the life of the alarm. ''Intelligent sensing technology'' system is designed to reduce nuisance alarms. ''Latching alarm indication'' remembers which unit initiated an alarm. When interconnected in a series, the unit that triggered the alarm rapidly flashes its red LED indicator. After the alarm condition subsides, the initiating unit will store in memory or ''latch'' the information and begin to flash the LED indicator 2 seconds on, 2 seconds off. The ''perfect mount'' system features a gasketless base and a mounting bracket that keeps the alarm secure over a wide rotation range to allow for true alignment. Other contractor preferred features include a dust cover to keep alarm clean during construction, keyhole slots in the mounting bracket eliminate the need to remove the electrical box screws for installation. Two locking features are provided to prevent battery theft and/or theft of the unit. Connection to AC power is made with a ''quick connect'' Wiring harness. Installation is quick, easy and cost effective.Hardwired Smoke or Carbon Monoxide Alarm Requirements: 120V household electrical circuit (unswitched 120VAC). Standard wiring junction box to a 4 in. (10 cm) size, on either the ceiling or wall.Selecting an appropriate location to install your smoke and carbon monoxide alarms.