Wearing an Apple Watch has become the difference between life and death for a New York man who never expected that buying one could save his life.

James Green, a 28-year-old from Brooklyn, describes himself as a serial data tracker. When he bought the original Apple Watch two years ago, he picked it up mostly for the notifications and tracking bike rides. Now, thanks to a heart-tracking app, it’s become a big part of his health story.

Heart not beating quite right? There’s an app for that.

Researchers for medical device company HealthSTATS International — in association with University College London — have patented the software behind what they claim to be the world’s first app to test for erratic heartbeats.