The First Alert CO615 dual power carbon monoxide plug in alarm alerts you to dangerous carbon monoxide. This carbon monoxide detector operates on a dual power system with battery backup for continuous monitoring, even in the event of a power outage. The backlit digital screen tells you at a glance what the carbon monoxide and power Levels Are. The Co monitor also features a convenient test and silence button and an end of life timer that lets you know when it is time to replace the unit.*ensure the outlet has power.*the battery is for back up only and is not intended to power the alarm for an Extended period of time in the absence of AC. *the alarm will light up the display briefly to indicate the unit is receiving power. *press and hold test button to ensure activation.