Front-load battery door – For quick battery replacements Ionization sensing technology - hardwired smoke detector senses invisible fire particles, 85 decibel alarm alerts of fire Whole home detection - easily install 1 fire detector on each level of your home & in each bedroom Still works during power failures - smoke alarm with battery backup operates on a 120V power source with 9V battery included Test/Hush Button – It’s simple to test or hush false alarms by pressing the button right on the face of the device UL Certified, 10-year limited warranty Package contains 4 Kidde smoke detectors