ORANGE COUNTY, Fla. -- They couldn't smell it, taste it, or see it, but there was enough carbon monoxide to make a family sleep late and it could have killed them.

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The College Park home was filled with the potentially deadly gas. There was a carbon monoxide detector, but there weren't any batteries in it. Needless to say, it was a close call for the brother and sister and their dog, Calhoun, who live in the home.

It turns out their 13-year-old hound dog was their carbon monoxide detector. He started feeling the worst effects of it first. Calhoun is Jerry Wood's prized companion and has been for all of Calhoun's 13 years. But he's in poor health and he was the first to feel the crippling effects of the carbon monoxide.

"My dog, Calhoun, the world's greatest hound dog, was sick and he just kind of passed out on me," Wood explains.

That's when Wood knew there was something serious wrong. He wasn't feeling so well himself. He was lethargic and was having trouble walking. Then he realized his sister was sleeping in just a little too late.

"When I tried to get up, I could hardly walk and I had gotten up at five in the morning with rapid heart beat," says Linda Ford. The cardiac care nurse called in sick, then went back to bed.

Firefighters say if Calhoun hadn't shown signs of illness, they would all be dead. With carbon monoxide, 35 parts per million can be deadly. Their house had 50 parts per million.

Firefighters have advice for people who have gas furnaces.

"Get an alarm. They're cheap. It's easy and it could save your life," says Lt. Danny Wilson.

The alarm could've saved Wood, Ford and Calhoun, if they had put a battery in it. There is a battery in it now.

Wood also credits the firefighters for getting on the scene quickly and knowing immediately what was wrong. They came in with a carbon monoxide detector and got every one out of the house right away.