Carbon monoxide (CO) is an invisible, odorless and tasteless gas. It’s produced by partial fuel combustion usually caused by insufficient oxygen. In your residence, appliances that need natural gas, charcoal, wood or kerosene are at risk. Especially if they are not operating properly or have been installed wrong.
Vehicle exhaust fumes from neighboring garages, as well as fireplaces that aren’t working right could also be a carbon monoxide source. CO is toxic to the body and is fatal at increased levels or with prolonged exposure.