Q: Apple Watch Alarms Turn Themselves Off

Hi

The following steps may help:

• Restart both your iPhone and your watch, turning both off together, then restarting your iPhone first:
  • Restart your iPhone, iPad, or iPod touch - Apple Support
  • Restart your Apple Watch - Apple Support

• Unpair and re-pair your watch:
  • The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app. Choose to Restore from Backup during set up. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
  • Unpair your Apple Watch and iPhone - Apple Support
  • Set up your Apple Watch - Apple Support

If the issue persists - which it may do, as another user has reported experiencing the same issue even after following those steps - I suggest that you contact Apple Support or make a Genius Bar reservation for assistance. Be sure to make clear that the issue has arisen in conjunction with updating to watchOS 3:

• Contact - Official Apple Support
• https://twitter.com/applesupport
• http://www.apple.com/retail/geniusbar/