Carbon monoxide (CO) is called the silent killer for a reason. You can't see it or smell it, but it can make you very sick — or even be deadly. Every year, more than 400 people in the United States die from carbon monoxide exposure, and thousands more get sick and need medical care.1November is National Carbon Monoxide Awareness Month. It's a good reminder to check your home, car and workplace for ways to prevent CO exposure. All CO poisonings can be prevented.What is Carbon Monoxide?Carbon monoxide is a colorless, odorless, poisonous gas produced by: