This BRK® alarm is a 120 V hardwired smoke alarm utilizing a patented photoelectronic smoke sensing technology that allows 360° access to the layer of air on the ceiling or wall that carries the signs of fire such as smoke, combustion particles and volatile components. This unit features a 9 V battery backup to ensure operation during a power failure and alarm indication that automatically identifies which unit in an interconnected series initiated the alarm. The alarm can be interconnected up to 12 smoke alarms. It also comports locking mechanisms for the battery compartment and base as well as a single silence/test button. This product is backed by a 10-year limited warranty.