I just got an Apple Watch SE and wondering if it needs water lock to be submerged
Apple Watch SE, watchOS 8
The water lock disables the touch screen and the side buttons so that you do not accidentally "Butt Dial" or activate other Apple Watch features due to water splashing on the Apple Watch.
The water lock does NOT add any extra water protection.
If you are washing your hands and you get your Apple Watch wet, that is not an issue if it it just clean water. You should avoid soaps and lotions getting on your Apple Watch as you can damage the water protection seals.
The answer in a nutshell is if you start a swimming workout the screen is locked. I suppose water lock turns on in theory too. Having said that - I just had my second Apple watch - an SE - fall apart during a swim. Screen came unglued. My previous watch, a Series 3, was a few years old so I thought it had just lost water resistance over time. The SE had not been for a swim in over a year. I am not sure now whether to get a different device completely or just one for swimming. Either way, not swimming with an Apple Watch again.
What about when I’m hand washing?
Is Water Lock optional when going swimming?
