Carbon monoxide is an odorless, colorless gas that is often undetected. More than 400 people in the U.S. die every year from unintentional carbon monoxide poisoning, and thousands more are hospitalized. When gas builds up in enclosed spaces, people or animals who breathe it in can be poisoned. Consider installing a battery-operated carbon monoxide detector, and have your furnace, water heater, and other gas or coal-burning appliances serviced regularly, along with your chimney. Click Here for More Information.