First Alert Hard-Wired w/Battery Back-up Ionization Smoke/Fire Detector 18 pk18 pc Hardwire Ion Smoke Alarm Contractor Pack Hardwired smoke detectors are wired directly into your homes electrical system. Detector includes battery backup and mute button. Battery backup ensures alarm works even during power outages. Mute feature silences nuisance alarms from cooking smoke or shower steam and single button tests alarm functions. Easy access drawer for battery: no need to take down alarm from ceiling to change battery.