Battery-Operated CO Detector senses and warns you of deadly, odorless, carbon monoxide. Carbon monoxide (CO) is a deadly, colorless, odorless gas created by faulty gas heaters, furnaces or automobile exhaust. But because it's odorless, without plug-in or battery-operated CO detectors there's no way you could know if deadly carbon monoxide was seeping into the air you breathe. Our Universal CD-9000 battery operated CO detector senses that gas, and sounds a loud alarm to warn you and your family. Wall-mounted CO2 detector sits in its mounting bracket included. Also includes silence/test button and batteries..