This First Alert hardwired smoke alarm includes a 9-volt battery backup that continues to protect you in the event of a power failure. The detector features an ionization sensor for detection of smoke and fast-flaming fires, as well as a loud, 85-decibel alarm. One button silences any nuisance alarms, and also tests detector functions, while lights indicate if the alarm detects smoke. The latching alarm indicator automatically identifies which unit initiated the alarm, even after the conditions that set off the alarm have subsided. And an end-of-life signal enhances your safety by letting you know when it's time to replace the unit. Connect it to compatible BRK or First Alert alarms within a single-family residence. When one alarm is triggered, all connected alarms will sound.