The Kidde 900-0113 (Model KN-COEG-3) is a 120 V AC powered, plug-in carbon monoxide, propane and natural gas alarm with battery backup and a digital display. The 900-0113 is an easy to install unit that provides reliable protection against the dangers of carbon monoxide. The gas sensor is a metal oxide sensor designed to detect natural gas (methane) or propane. Digital display: Shows CO level in PPM (parts per million) and detects "GAS". No buttons to push. Continuous digital readout gives you peace of mind at-a-glance Peak level memory - Displays the highest CO concentration measured since the last reset Tests the unit for proper operation and resets the alarm AC plug-in operated: easy to install, just plug into an AC wall outlet 9 V battery backup provides continuous protection in case of a power failure