Alarm plugs into any standard 120 VAC outlet with no additional mounting and battery operated alarm back-up provides consistent protection for added safety during power outages. Mute button mutes unnecessary alarms and tests alarm functionwith same button. Easy access battery door has a front-open compartment that allows easy battery change without dismounting alarm. Low battery signal mute quiets low battery signal for up to 8 hours. (1) 9 volt battery included. Loud 85 decibel alarm. 7-year limited warranty.