The software will use machine learning to detect motion that resembles handwashing, before activating the microphone to check for audio cues like running water or splashing. Once it’s confident you are washing your hands, it’ll start a countdown and measure your sink time to make absolutely sure you did make it to the end of that second ‘Happy Birthday’, pestering you if you don't make it to the end.
There's also the option to use location-tracking to enable alerts to remind you to wash your hands whenever you return home.
The other major addition to watchOS 7 is sleep tracking - a long-requested feature that most rival smartwatches have supported for some time. Apple’s iteration will measure both the duration and quality of your sleep, wake you with a silent haptic alarm, and give you an alert in the morning - including a reminder to charge the Watch back up, since it’ll probably need it.
Elsewhere the Activity app has been re-branded Fitness and throws in some extra workouts like dancing and strength training, watch faces can now be customised and shared, and the Maps app supports the same cycling routes added to iOS 14 - in select cities.