Battery-operated carbon monoxide (CO) alarm provides continuous monitoring of CO levels and 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 and resets carbon monoxide alarm. Red LED will pulse and 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. Easy-to-install alarm is suitable for all living areas. Alerts user to replace CO alarm after seven years of operation. Quick-reference guide on inside cover of battery door.