Plug-In CO (carbon monoxide) alarm utilizes an electrochemical carbon monoxide sensor to detect carbon monoxide. The plug-in design of this personal carbon monoxide detector means you can simply plug the alarm into a 120-volt wall outlet， and the carbon monoxide detector is ready to go. When CO levels become elevated， a loud 85-decibel alarm alerts you to the threat. Designed to be simple to use， the CO detector has just one button that silences or tests the unit， as well as an end-of-life timer that lets you know when it is time to replace the device. White. UL (Underwriter's Laboratories) listed. 7-year limited warranty.