First Alert CO400 Battery Operated Electrochemical Carbon Monoxide Alarm utilizes an electrochemical carbon monoxide sensor to detect carbon monoxide. This carbon monoxide detector is battery operated, making it portable and easy to use, even in the event of a power outage. When carbon monoxide levels become elevated, a loud 85-decibel alarm alerts you to the threat. A low-battery light and alarm alert you when battery power is running low, and an end-of-life timer lets you know when the device should be replaced. Each CO detector lasts approximately five years. Simple set up - simply insert the battery, and the CO detector will start to monitor your space for carbon monoxide. There are no complicated displays or settings to navigate. A single button silences the alarm and tests the CO detector. A pull-down action chart instructs you of what to do if the CO alarm goes off.