Asking people to remove watches - especially metallic ones - is common across airports and there is frankly no reason to wait till it first sets the alarm if you know it will.

theft at security checkpoints was (and possibly still is) quite common at US airports where you didn’t use to need to show a bp to go through and can exit immediately. Two accomplices, one before and one after an expensive looking target. First one goes through (usually wearing a cap or so to hide as much as possible from cameras) smoothly but slowly. The one behind the victim has very few things to take off but goes to the security gate after the victim has emptied their first expensive possessions but before them. They set the alarm and ‘realise’ they have forgotten their belt, then their keys etc wasting as much time as possible, thereby enabling accomplice no1 to disappear with anything worthwhile amongst the victim’s possessions and disappear. Accomplice no2 then goes through and disappears (with his/her own property) before anyone realises what happened.

there were sadly lots of victims in the late 90s early 2000s but hopefully the extra checks now will have made this rarer.