Carbon monoxide alarm plugs directly into a standard wall outlet to make installation quick & easy. Battery backup uses two AA batteries (sold separately) for complete protection even during power outages. Tamper-resistant design alerts you if it has been unplugged or has come loose from the outlet. Two LEDs illuminate to show you when it's in alarm mode or normal mode. Test / reset button tests the circuit operation & allows you to immediately silence the alarm. End-of-life alarm conveniently alerts you to replace the unit after 10 years of operation.