I find that tiredness is my main trigger, and that an alternative thing to busy my non-dominant hand with is the only thing that helps once I've got the urge.
A fidget cube, as mentioned upthread, is a good idea, but personally I find them too far to reach to when the trance descends, so I use jewellery instead.
I used to have people ask about it, years before I found out that it was a proper disorder, with a name and identifiable causes. And what I hated most about that was how demanding they were about it, as if I was choosing to do it on purpose to freak them out, or something. It always made me feel so angry and powerless.
These days I'd just name it and give them a couple of sentences about what trichotillomania is, because I'm very comfortable with my disabilities and don't feel at all embarrassed about things I can't help. Also I like to raise awareness where I can, especially in case anyone present is also struggling with it.
I know it's not that simple for everyone, though, so if nothing else, talking therapy might help you gain more self-acceptance over this, and confidence in talking about it.
And those things can themselves relieve your stress a little, and help you feel good about pursuing any accommodations or changes to your appearance that you'd like to make to deal with the problem.