First Alert CO400 Battery Operated Carbon Monoxide Alarm DetectorProduct Description The First Alert CO400 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,