First Alert CO400 Carbon Monoxide Detector, Battery Operated Keep your family safe with this easy to use, battery operated carbon monoxide alarm; battery powered alarms provide continuous monitoring of CO levels, even if there's a power failure Features an advanced electrochemical carbon monoxide sensor that accurately detects carbon monoxide levels, no matter where the detector is placed in the room A loud 85-decibel alarm sounds when CO levels reach dangerous levels To ensure complete protection make sure to place one on each level of your home and in each bedroom 5-year limited warranty; equipped with end-of-life signal chirp, so you know when its time to replace the unit for safety All First Alert CO alarms are rigorously tested to meet UL standards