First Alert Carbon Monoxide Alarm NWT

First Alert Carbon Monoxide Alarm New in package Model: First Alert CO605 Plug-In Carbon Monoxide Alarm with Battery Backup (Cat. 1039734). Power Source: It is a plug-in alarm that also includes a 9V battery for backup power during outages. Sensor: The alarm uses an electrochemical sensor to detect carbon monoxide. Features: It has a test/silence button and an end-of-life warning to let you know when it's time to replace the unit. The sensor has a 7-year limited warranty.