Shop for Electrical . The First Alert CO400 battery powered carbon monoxide detector with mute button is an easy-to-install, UL-listed alarm that combines advanced technology with a user-friendly design. Symptoms of carbon monoxide poisoning are like the flu, and you might not even know you're in danger. That's why a carbon monoxide alarm is an excellent way to protect your family. It detects the CO you can't see, smell or taste in the air. A single button tests alarm functions and mutes nuisance alarms. This alarm uses an electrochemical carbon monoxide sensor, which is the most accurate technology available. With battery backup, you will have peace of mind that the alarm will continue to work even when the power goes out. It's esthetically pleasing premium shape is ideal for placing in all visible location. The easy loading front access battery door allows you to quickly and easily change the alarms 2 AA batteries. 5-year limited warranty. Meets UL standards and is code compliant.