.The First Alert CO605 carbon monoxide alarm uses an electrochemical sensor the most accurate technology available. The permanent sensor lasts up to 5 years. This carbon monoxide alarm plugs into any standard electrical socket and monitors your space for elevated carbon monoxide levels. The test/silence button silences the alarm and allows you to test its functionality. The unit monitors and re alarms if carbon monoxide level persist sounding a loud 85 decibel horn. This CO detector also features a battery backup that allows for continuous monitoring, even in the event of a power failure. The simple, user friendly design makes this CO detector easy to setup and operate, and it features an end-of-life warning that lets you know when it is time to replace the unit.