simple way to avoid issues is to always put your watch or whatever valuables you have inside your bag in the security preparation area

Waiting for the beep at the scanner for stuff you know will set it off just delays everyone else.

Don't be that person* that delays everyone else.

(* FT rules prevent me from giving an accurate description of such people but it involves combinations of 4 letter words)

Clearing security is not hard if you are ready. Unfortunately a lot of people - especially frequent fliers - don't think the rules apply to them.