Carbon monoxide, or CO, is a colorless, odorless, toxic gas. It is produced by the incomplete combustion of solid, liquid, and gaseous fuels. If such appliances are not installed, maintained, and used properly, CO may accumulate to dangerous and even deadly levels in cars, homes, or poorly ventilated areas.
Carbon monoxide is produced by devices that burn fuels.
Therefore, any fuel-burning appliance in your home is a potential CO source. Electrical heaters and electric water heaters, toasters, etc., do not produce CO under any circumstances. Under normal circumstances, CO should not be detectable in the typical home or workplace. Likewise, using kerosene heaters or charcoal grills indoors, or running a car in a garage, can cause levels high enough to result in CO poisoning. Any person or animal in space shared with a device capable of generating CO should be considered at risk of CO poisoning.