During a keynote at Apple's Worldwide Developers Conference, the company debuted the latest version of WatchOS, the operating system that runs on the Apple Watch.

Apple claims that it has improved the Apple Watch's ability to detect arterial fibrillation (AFib), an irregular heartbeat that can lead to blood clots, stroke, heart failure, and other heart-related complications. With the arrival of WatchOS 9, supported Apple Watch device models can now detect "burden," or how often a person experiences AFib over a certain amount of time.

Apple was granted 501(k) approval from the U.S. Federal Food and Drug Administration this morning. As opposed to full approval, 501(k) approval doesn't require companies to provide effectiveness data from clinical trials.

With WatchOS 9, supported Apple Watch models now show heart zones to get a sense of your intensity level. You can set up distance and time intervals, and there's haptic and voice feedback to tell you when to switch modes when working out.

New complications and watch faces (including a new astronomy face and a new lunar watchface with support for various lunar calendars) and exercise modes are a part of the WatchOS 9 release, as well as new "form metrics" for runners (the Apple Watch's accelerometer and gyro figure out your running form, stride length, and ground contact time). There's a new workout type for triathaletes that can auto-switch between cycling, swimming, and running.

Joining these are a new sleep-tracking feature: Sleep Stage. WatchOS 9 can detect REM, core, and deep sleep stages. And -- via the revamped Health app on iOS -- new women's health and medication-tracking services. And for users who own a Meta Quest VR headset, Apple Watch now shows stats from Move, Meta's fitness tracker for the Quest, on the Fitness mobile and Watch app, listed under Fitness Gaming.

Rounding out the health features, WatchOS can now track medications and notify wearers when they need to take them. Most of the management is done via iOS in the Apple Health app, where you can scan a medication label to identify it.