The Apple Watch Series 3 is more health-focused than ever, coming packaged with an improved heart rate monitor, and an interesting but mysterious medical study.

Apple COO Jeff Williams unveiled the device Tuesday at the iPhone Event, along with a new watchOS and workout app.

The heart monitor will monitor a slew of new metrics, including resting heart rate and recovery heart rate after exercise. (You want a lower resting rate, and a higher recovery rate).

Your Series 3 will also alert you when your resting heart rate is elevated while you don't appear to be active. The new feature is "inspired by a lot of the letters we receive from customers who notice an unusually high heart rate when they wouldn't expect one," according to Williams. "Most people won't notice."

Williams didn't elaborate on the circumstances in which people found their heart rates rising unexpectedly. A rise in heart rate could be caused by such things as pregnancy, caffeine, or anxiety, in addition to more serious issues.

Apple has also partnered with Stanford University to conduct the Apple Heart Study, which will utilize heart rate data collected by the Apple Watch to study heart arrhythmia (an irregular heartbeat), a severe form of which, atrial fibrillation, can lead to life-threatening complications if undiagnosed.

"We've been looking at this for a couple of years, and we think Apple Watch can help," said Williams. He claimed that in previous studies, the Apple Watch has been successful in identifying arrhythmia in users.

Apple Watch users will be able to sign up for the study, and it will be available in the app store "later this year," according to Williams. Researchers will then use data collected by the Apple Watch to "analyze arrhythmias and notify users."

The specifics of this research are, again, a bit hazy. The exact question being researched, the nature of the information users will be receiving, and the potential privacy concerns remain, for now, a mystery.

What we do know is that both features are part of a renewed push from Apple to cement the Watch as a staple of fitness and health.