Working smoke alarms cut the risk of dying in a home fire by 50%, and that"s important because a home fire starts every 83 seconds! The faster you know about a fire, the faster you can start moving your family outside. First Alert"s SA9120BCN alarm with battery back-up uses ionization smoke sensing technology and sounds an 85-decibel alarm. A power indicator on the unit confirms that it is receiving power and a silence/test button checks all alarm functions and silences a non-threatening alarm. If the wired-in power is malfunctioning, the 9-volt back-up battery powers the unit. The battery is easily installed in a pivoting side load battery compartment. The universal mounting brackets are designed for easily installation and help to hide drywall cutouts. The mounting system includes a gasketless base and mounting jacket. The alarm contains an optional pin to lock the battery and unit in place for tamper resistance. When the alarms sound, the latching alarm indicator identifies which unit initiated the alarm, alerting you to the area of danger. The alarm includes quick plug-in connectors for easy installation and can be interconnected with up to 12 compatible smoke alarms and 6 additional units. If one smoke alarm in the series triggers an alarm, they will all sound. AC-powered smoke alarms must be installed in accordance with all local electrical codes, and should only be installed by a qualified electrician. This alarm includes one 9-volt battery and comes with a 10-year limited warranty. Approved for sale in Oregon after revisions to Governor"s law. Replaces old #SA4121CN.--Bree NorlanderWhat"s in the Box One smoke alarm, user"s manual, and one 9-volt battery