When it's chilly outside, naturally, we try to get warm.
"Any type of manmade heat, whether it's a fire or a furnace, a gas stove...any time you have combustion, you produce carbon monoxide," said Ross Tobleman, with the Round Rock Scott and White Hospital.
He says carbon monoxide is a "silent killer."
"It's a colorless, odorless, tasteless gas that people don't know is in their house," Tobleman added. "People will start to get nauseated, people will start to have headaches, fatigue, lethargy, confusion...ultimately, they'll pass out and they can die."
That's why it's important for everyone to have one of these, a carbon monoxide detector. You can see there's a wide variety available and this one, it's a combo, smoke and carbon monoxide detector.
Tobleman said, "I recently had a couple that came in and left their car running in their garage, went and played cards and didn't really recognize that anything was wrong until the husband noticed that his wife passed out and was starting to feel the same symptoms and luckily, he was able to call 911 just in time."
The carbon monoxide can even reach you from a neighbor's home, like a poisoning that happened at an Austin apartment complex in June 2012.
"Typically, we'll see...five to ten people a year that come into the emergency department with carbon monoxide exposure," said Tobleman.
The couple that recently visited this emergency room, had no idea it was co poisoning.
Tobleman said, "Literally, they were both within minutes of dying."
"I have a carbon monoxide detector in my house and I don't have anything that really produces carbon monoxide...but I still think it's that important because you don't know," he added.
It's always better to be over-prepared, just in case.
According to the Centers for Disease Control and Prevention, more than 450 people die each year in the U.S. from CO poisoning.