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REEDSBURG, Wis. — You won’t see it and you won’t smell it, but it can kill you. Every year, on average, 430 Americans die from carbon monoxide poisoning, according to the CDC.

And if you think having a CO detector in your home will keep you safe, just ask a Wisconsin family who are alive only because they were saved by grace — their cat.

As any cat owner will tell you, sometimes you wonder who owns who.

“We have three cats, and all three of them do run the house,” Kevin Shanahan said. “We’re just here to feed them and take care of them.”

Sometimes a cat like Gracie returns the favor and takes care of them, like the time around 1 a.m. when everyone was sound asleep.

“All of the sudden Gracie, I heard she was pounding, knocking, knocking, knocking at the door,” Shanahan said. “And so I got out of bed and to stop her from pounding at the door, and I looked to my left and Annette was there in the chair.”

“I was hanging onto the arm of the chair, and I thought I was dying,” his wife Annette said.

“And she called 911, and all she could say was ‘can’t breath.'”

When firefighters arrived, they discovered lethal levels of carbon monoxide in the home. It was caused by a malfunction in the hot water heater.

Annette and Kevin were taken to the hospital, where they spent the night.

Had it not been for Gracie — well, they’d rather not think about that.

“Very lucky. If it wasn’t for the cat, I don’t know how much she was saving our lives, but she wanted to get out of there, and she knew enough to know something was wrong, and she was pounding on the door.”

And if you’re thinking they should have had a CO detector, they said — though it was 15 years old.

Manufacturers recommend they be replaced every five years. The family now has four new CO detectors — or maybe it’s five counting Gracie.

The family forever will have a new appreciation for an old saying: saved by grace.

“I say saved by grace, saved by the grace of God, because she doesn’t usually sleep with us,” Annette said.