Carbon monoxide (CO) is a tasteless, odorless gas that is the leading cause of accidental fatalities by poisoning in the U.S. This dangerous gas is the byproduct of incomplete combustion or burning of materials that contain carbon such as natural gas, propane, oil, kerosene, and wood. CO poisoning can be present at unsafe levels without occupant awareness if CO detectors are not in place.
 
The presence of carbon monoxide in the air, even at just .1%, can adversely affect concentration, with levels at only 2% causing a reduction in breathing rate of up to 50% and CO levels at 5 to 10% quickly causing unconsciousness. CO detectors should be used in residential homes, and commercial grade CO detectors must be used in commercial properties. The City of Chicago also has carbon monoxide detector installation requirements for owners of residential property and commercial properties.