Battery Operated. Uses three AA batteries. The easy opening cover gives fast access to the batteries. Fuel cell sensor. The electrochemical sensor contains a proton conducting membrane which generates a current in the presence of carbon monoxide (CO). This current is measured; information is processed and then displayed on the alarm. The sensor is more accurate, uses less current and is less sensitive to humidity and other gases than competitive models. This technology was developed and patented by Atwood Mobile Products. Loud alarm and digital display. Updates CO level read-out every 15 seconds. Peak level displays highest concentration detected. Long battery and sensor life. Wall or ceiling mountable. Multiple location. A picture frame leg allows you to use the CO Alarm at multiple locations. Ideal for locating the CO source or for additional security when sleeping in another room. Safety feature. Cover is designed with a safety feature that makes it difficult to close the cover without batteries in the unit. This helps to prevent the alarm from being mounted without power.