Although Apple Watch is not listed this topic seems to fit this forum better than any other. I have just upgraded my Apple Watch 4 to Watch OS 5.1.2 and it no longer responds to raising my wrist — I have to tap on the face to activate the watch. I have checked the settings both on the watch and the watch app on my iPhone and the orientation and left or right arm is correct, and the settings to activate on wrist raise are also correct. I have tried the universal cure (rebooting) twice, all to no effect. A quick DuckDuckGo search did not turn anything useful up. Any suggestions before I give up and make an appointment at the Apple Store?

FWIW, my Series 4 made the update without issue.....have you reset the watch to factory defaults (nuclear option) to see if it will re-initialize once you reconfigure?

I will give it a try and let you know how it works out.

I fixed it without going to the full Nuclear Option but close to it. The procedure was...

1. In Settings > General > Wake Screen turn all the options OFF
2. Reboot the watch
3. In Settings > General > Wake Screen turn "Wake screen on wrist raise ON"
4. Reboot watch
5. Screen now wakes on wrist raise as it should

AFIK the reboots are essential to the process 🤷‍♂️

Glad to hear it.....the only glitch I experienced with the new Watch OS 5.1.2 update (and the associated iOS update to 12.1.1) was my AirPods going flaky and losing sync between the iPhone X and the new Series 4 Apple Watch. Forgetting the AirPods on the iPhone BlueTooth Settings page, then resetting the AirPods and re-pairing to the phone made it all "just work" again.

These posts are good reminders that even with non-computers, sometimes a "restart" is the answer.

True, but don't forget the Apple Watch is a very powerful albeit compact computer with a watch dial, stem, and touch screen for the user interface. Even the first Apple Watch was capable of running MacOS 9 (someone tried it and it worked).