Are you a proud owner the of the Apple Watch Series 2?
Try this: With the screen off, turn the Digital Crown towards the top of the display. Neat, right?
With the Series 2, Apple has added a feature called "Wake Screen on Crown Up." As you just saw, you can turn the crown up to slowly wake the screen, to discreetly check the time in a movie theater or in a meeting. As you scroll down with the Digital Crown, the display's brightness decreases.
You still have the option to raise your wrist to or tap on your watch's display to wake the screen, of course.
You can disable the new feature in the Watch app on your iPhone, under General > Wake Screen > Wake Screen on Crown Up.
Source:
https://www.cnet.com/how-to/quick-tip-discreetly-check-the-time-on-your-apple-watch-series-2/