Carbon Monoxide is an odorless, colorless gas that is very toxic and deadly. When appliances that rely on fossil fuels, such as kerosene or gas, malfunction, they can emit carbon monoxide. This is dangerous in the home and can be a silent killer. A carbon monoxide detector will detect the gas in the air in a room and make a sound when the gas is present. Carbon monoxide detectors last about five years. You need to change the battery every year.