The ink, pattern and/or saturation of some wrist tattoos can prevent the Wrist Detection feature on Apple Watch from working.
It may help to wear your Apple Watch a little higher up or lower down your arm.
It may otherwise help to wear your Apple Watch on your other wrist. Even if you also have a sleeve tattoo on your other arm, it may still be worthwhile testing this. The nature of that tattoo may vary sufficiently to allow expected operation on your other wrist. To change the configuration of your Apple Watch accordingly:
On your iPhone, in the Watch app, go to: My Watch (tab) > General > Watch Orientation > choose the preferred wrist and side for the buttons.
Otherwise, whilst turning off Wrist Detection and passcode would avoid undesired locking of your Apple Watch, you would no longer be able to benefit from features including using Apple Pay, earning Stand credit and the convenience of a single unlock after placing your Apple Watch on your wrist.
If you would prefer to have your Apple Watch checked for any potential hardware issue, then I suggest that you contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider with a view to arranging that:
- US: Apple Watch Service Answer Center - Apple Support
- Elsewhere: Select your country for Apple Watch service and repair information