The Ei3018 is a Carbon Monoxide (CO) Alarm powered by 230V AC mains power, and has built in tamper proof rechargeable lithium cells that act as a battery back up in the event of mains failure. These rechargeable lithium cells are designed to last the life of the CO alarm.
Green - Power. Red - Pre-alarm/ Alarm/Silence mode/Memory. Yellow - Fault/ End of life.