A support document Apple published earlier this month contains a number of interesting tidbits and nice-to-knows regarding the Watch's built-in heart rate monitor. We thought it'd be useful to give you a quick summation of the technologies the wrist-worn device uses to provide accurate readings of your heart rate.
The document also confirms that the Watch can connect wirelessly to external heart rate monitors such as Bluetooth chest straps for even more precise readouts.
All in all, Apple's done a fine job outlining in Layman's terms the tech and the sensors that measure a user's heart rate, a feature many reviewers have described as seamless. In Apple's parlance, it just works and here's exactly how it works.