This turned out to be the best Christmas gift ever.

13-year-old Austin Hardison lives in Arizona, and asked his mom for a smartwatch last Christmas, because a few of his friends had gotten them.

And this summer, it ended up saving his life.

He was watching TV recently, when he started to feel light-headed. Then he looked at his watch, and it said his heart rate was 219 beats per minute. Which is way high.

A normal resting heart rate is between 60 and 100 beats per minute. And at his age, it should never be higher than about 200. But that's if he was running, or doing vigorous exercise. Not sitting on the couch.

His mom thought he was just anxious about school starting back up. But she took him to the doctor. And it turns out he was born with a heart condition they didn't know about.

He might not be able to play high-impact sports because of it. But now his doctors can treat it. So his watch probably saved his life.

Read more at KNXV.