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 NY, 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.

Green was unknowingly suffering from a pulmonary embolism when he had his Apple Watch on. His wrist lit up with a notification from HeartWatch. Cross-referencing that data with the some of his past heart rates, he realized his heart rate was higher and something might be seriously wrong.

Never thought a stupid lil wrist computer I bought 2 years ago would save my life. Saw my ❤️ rate go up, ended up being a pulmonary embolism pic.twitter.com/r97uRcX0En

— renata’s eyepatch (@_jamestgreen) October 13, 2017

Using the Apple Watch, Green developed a habit of tracking all of his data such as food, water, sleep, and heart-rate. He had a pulmonary embolism a few years before he got an Apple Watch, but having quick access to the data proved invaluable.

“It was cool to open up the health app and show it to my physicians and give them more data to work with,” said Green. “I had no idea this watch would save my life.”

Apple Watch has saved the life of a number of wearers over the last two years. Even though it’s not registered with the FDA as a medical accessory. New sensors and tech could make the wearable even more valuable in the future to owners. The FDA has also created a fast track for medical products to help Apple and a few other companies innovate faster in the field.

Researchers measured Apple Watch as the most accurate heart rate monitor among smartwatches. During the company’s iPhone X event, Apple released a video of Apple Watch wearers sharing their stories on how the device helped them live healthier lives.