CO615/FCD4CN-3 PREM CARBON MONOXIDE DETECTOR | 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.