Twitter user Daniel Marcinkowski spotted the yet-to-be-released Sleep app for the Apple Watch mentioned in an App Store listing. The reference popped up for Apple's pre-installed Alarms app on the Apple Watch. Check out the screenshot below, which shows an unreleased version of the Alarms app labeled with "Sleep" and a recommendation to "set your Bedtime and wake up in the Sleep app".
While there is no mention of this so-called Sleep app in the new WatchOS 6.0.1 update (or WatchOS 6.1 beta), MacRumors recently noticed evidence of it in an internal build of iOS 13. Specifically, it spotted a sleep-tracking feature called "Time in Bed tracking". One code string noted users could track their sleep and "get woken up silently" by wearing their Apple Watch to bed.
9to5Mac said Apple has been developing this sleep-tracking feature so that it can monitor sleep quality via sensors within the Apple Watch. They'll log a user's movement, heart rate, and noise, and all the data will be delivered into the Health app and of course also made available in the new Sleep app for the Watch, which will serve up an overview of sleep patterns with bedtime reminders.
It's expected that, when the Sleep app releases alongside the Time in Bed feature, a new watch face will also become available. Bloomberg's Mark Gurman, who has also claimed Apple is testing sleep tracking on the Apple Watch, said Apple plans to roll out the feature by 2020.