The First Alert CO400 carbon monoxide alarm utilizes a electrochemical carbon monoxide sensor that lasts for up to five years to detect carbon monoxide. This carbon monoxide detector is battery powered, making it portable and easy-to-use anywhere, even in the event of a power outage. When carbon monoxide levels become elevated, a loud 85 dB alarm alerts you to the threat.

• CO detector alerts you to carbon monoxide
• Electrochemical CO sensor is most accurate technology available
• Battery-operated design works almost anywhere
• Loud 85 dB alarm sounds when CO levels are elevated
• Single test/silence button for simple operation
• When carbon monoxide levels rise, the carbon monoxide detector sounds an 85 dB siren that is designed to wake even the soundest of sleepers
• 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 5 years

• https://assets.unilogcorp.com/187/ITEM/DOC/FIRST_ALERT_100093181_Owners_User_Manual.pdf Owners/User Manual