Apple Watch can automatically detect when you start hand washing using its motion sensors and microphone and intuitively launches a 20-second timer.
Your Apple Watch listens for the sound of soap and water running to determine whether or not you are washing your hands.
If the watch also senses hand washing motions (rubbing your hands together), it assumes you are washing your hands.
Once detected, it starts a 20-second timer encouraging you to wash your hands for a full 20 seconds.
If you stop washing too early, your Apple Watch nudges you with an on-screen alert to finish for a full 20 seconds.
Once you finish washing your hands, your watch sends that data to your iPhone’s Health app and logs the time you washed your hands in the Health app’s Other Data section.
After this, it logs the full time you were washing your hands even if it was longer than 20 seconds to the Health app in the “Other Data” section.
Additionally, your Apple Watch can automatically remind you to wash your hands each time you get home.
Does it work with my Apple Watch?
Only if you have a Series 4 or newer.