One time, a TSA official told me "never take off your watch in an airport unless you want to lose it" -- which is how I learned that you can wear your watch through the metal detector just fine, which I've now done dozens of times.

Until a few weeks ago when a another TSA official berated me for thinking I could walk through a metal detector wearing a watch...

Proximity is the issue. If the watch or bracelet wrist is very physically close to the detector, it will set it off.

You're supposed to the watch/bracelet, but you do have to hold your wrist close to your body. You kind of want to hold your hands in front of your body as if you're about to grab one of your wrists with your other hand.

Watches and other jewelry are basically right at the cutoff of detection. They want to detect small knives but not earrings.

This is all absolutely tribal airport knowledge. I had been traveling for work for years, taken hundreds of flights, but I only found this out when my partner tried to go through a metal detector with a semi-permanent bracelet that requires a small screwdriver to take off, and the TSA person mercifully told her exactly how to pose as she walked through the detector.

I just put my watch, wallet, phone and other loose or pocket belongings in my backpack or jacket that's already going in the tray. No chance of losing anything.

I was told this about my passport and wallet once. Then the other day asked if I could keep a tissue in my pocket and was told to put it in the tray. I think it depends on the scanners (if you’re going through a metal sector it’s fine, if its one of the more fancy scanners they need everything off your person.