There’s a feature of the Apple Watch Swimming Activity where a countdown appears on screen while a beeping noise appears and suddenly, the watch screen is locked and it’s time to swim! While this provides a nice official start to your workout, the only impact that locking the screen has is to prevent water from interacting with the screen.
Without getting into a long, scientific explanation about touchscreens and pool water, the Apple Watch touch screen is affected by the pool water. The Apple Watches use capacitative touch screens, which are activated by the changes in the electrostatic field across their surfaces caused by your conductive finger. Since pool water contains many dissolved ions, it is similarly conductive and can simulate touch. By locking the screen, Apple is preventing any “accidental touches” that the pool water may create that could disrupt your swim.
The Swim.com app has been designed in a way that touches on the screen only act to scroll between views while you’re swimming. Once you’re done your swim, the Swim.com app uses Force Touch to end the swim, which cannot be activated by the conductivity of the water alone.
But what about that nifty feature Apple demoed where water is ejected from the Apple Watch Series 2 at the end of the swim? That also has no effect on how waterproof your Apple Watch is, but it does clear the water out of the hole for the microphone/speaker so that the sound isn’t distorted. It’s a cool feature to have, but Apple doesn’t have an API present to enact it in our app at this time. You can start and end a Pool Swim from the Activity app to get the same benefit, but in our experience, the water clears out of the speaker/microphone hole pretty quickly anyway.
Short answer: No. Locking the screen has no impact on how waterproof your watch is.
If you’d like to find out more about Apple Watch 2’s water resistance rating and what you can and can’t do with the watch, please visit this article at Apple Support: https://support.apple.com/en-us/HT205000
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