Electrochemical carbon monoxide sensor. Plug-in with battery back-up, works during power outages. One button to silence or test alarm functions. Low battery silence quiets low battery alert without affecting alarm operation. Covers only one wall outlet. Loud 85-decibel alarm. Low battery warning. End of alarm life timer alarm chirps when it is time to replace, should be replaced every 5 years for maximum protection. 3.3" height x 4.75" width x 2" depth, 0.43 pounds. UL Listed. 5 year limited warranty. Uses 2 AA batteries, included.