The First Alert CO400A Carbon Monoxide Alarm utilizes an electrochemical carbon monoxide sensor to monitor your space for a carbon monoxide threat. The battery-powered design doesn't require an electrician; simply insert the included 9-volt battery, and the carbon monoxide detector is ready to go. The advanced electrochemical CO sensor detects carbon monoxide leaks from multiple sources, such as faulty fuel-burning appliances, blocked chimneys, and generators running inside or too close to homes. When CO levels become elevated, a loud 85-decibel alarm alerts you to the threat. Because CO evenly distributes itself, it's important to have a CO detector on every level and in every bedroom of your home. 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's time to replace the device.