Developers will be able to build widgets for existing watch faces (although not, apparently, entirely new watch faces). They’ll also be able to access the digital crown to peer back through the history of the information presented by widgets — an inning-by-inning baseball update, or calendar information.
In addition, developers will gain both read and write access to the watch’s mic and speaker, haptics, and accelerometer, as well as the Wi-Fi radio. That means the watch may be less tethered to a customer’s iPhone than it is today.
[Update: Apple, in a press release, suggests that, for instance, Strava will get direct access to your motion and heart rate data, and VW can give you haptic feedback when you lock your car. The company also announced a Nightstand Mode, where the watch will show the time and upcoming alarm time while it’s charging. Watch OS 2 will be ready in the fall.]
It’s still much less than clear what all this direct access will do to the Watch’s performance or battery drain.