The first alert brk 3120b hardwire dual photoelectric & ionization sensor smoke alarm with battery backup is designed to provide peace of mind. It features photoelectric & ionization sensors that detect not just fast-flaming fires, but also smoldering ones. The 85-decibel fire alarm has two latch options to indicate a low battery or the originating alarm in a system. It also offers a one-touch silencetest button & can connect to other compatible hardwired alarms for expanded coverage. This smoke detector includes optipath 360 patented technology that provides 360 degrees of access to the smoke alarm, as well as a battery backup for power outages.