Works during power outages. No installation required. Place or mount almost anywhere. Mute/test button to quiet unnecessary alarms, test alarm function. 85-decibel alarm, low battery warning. Low battery mute quiets low battery signal for up to 8 hours. Front-open compartment allows battery change without taking alarm down. Electrochemical sensor is the most accurate technology available for detecting carbon monoxide. End of life timer alarm chirps when it is time to replacethe alarm. Meets UL2034 standard. Uses 9 volt battery, included.