Battery-operated carbon monoxide (CO) alarm provides continuous monitoring of CO levels & will sound a loud warning signal if elevated CO levels are detected, even during power outages. Battery lockout system deters covering battery compartment without installation of batteries. Slide-out battery door cover gives immediate access to batteries. Test / reset button tests unit for proper operation & resets carbon monoxide alarm. Red LED will pulse & a loud alarm pattern will sound when a dangerous level of carbon monoxide is detected. Green LED flashes every 30 seconds, indicating unit is operating properly. Power Source(s): 3 AA.