Electrochemical sensor technology detects CO gas | Easy installation, no wiring needed, detects during a power failure by operating on 2-AA batteries (included); Install on a wall of your home or place on a tabletop | Green LED indicates power to the carbon monoxide detector, while an 85-decibel alarm & a red LED indicates the presence of carbon monoxide | Event Memory records the last time carbon monoxide was detected or when the unit was last tested