Keep your family safe without the hassle of battery-replacement & maintenance. The sealed-in battery keeps this carbon monoxide alarm functioning for ten years without the need for replacement. Easy to install alarm automatically activates when attached to the mounting bracket. Test / reset button tests unit for proper operation & resets carbon monoxide alarm. Green LED flashes every 30 seconds, indicating unit is operating properly. Red LED will pulse & a loud alarm pattern will sound when a dangerous level of carbon monoxide is detected. Red LED will also flash every 60 seconds if a high level of carbon monoxide has been detected within 14 days. Power Source(s): Lithium-Ion Battery; Mounting: Wall.