First Alert CO410 Battery Operated Carbon Monoxide Alarm DetectorThe First Alert CO410 Carbon Monoxide Alarm uses an electrochemical carbon monoxide sensor. Peak Level feature displays the highest concentration of carbon monoxide measured. When Carbon Monoxide levels become elevated, a loud 85 decibel alarm alerts you to the threat. Designed to be simple to use, the Carbon Monoxide detector has just one button that silences or tests the unit. Because CO evenly distributes itself, it's important to have a CO