Apple’s latest smartwatch, the Apple Watch Series 4, is a notable upgrade on previous models. It has a bigger screen, a better design and improved fitness performance. But the most interesting, and potentially life-saving, news is that it’s the first smartwatch from Apple to have ECG (that’s electrocardiogram) technology built-in.

ECG technology isn’t new. It’s been added to a number of smart, consumer-friendly health devices for some time now. Most notably AliveCor’s KardiaBand and KardiaMobile and QardioCore.

But now Apple has pressed the button on bringing ECG to mainstream wearables, others are following suit. The Withings Move ECG is on the way soon, packing ECG tech into a Withings hybrid. There are also plans for Alphabet to bring out the Study Watch, which will capture ECG and heart rate data, as well as much more.

ECG tech is here to stay. But what can it really do for you?