I am shooting a really fun psycho trigger these days, thanks to a recent Joel Turner/Push archery podcast.
I can put my tongue to the roof of my mouth with my lips sealed, and by building pressure with the tongue, make a variety of grunts/squeaking noises. no inhalation, just tongue/jaw movement. That's the basis for my trigger. This is all something I've been experimenting with for a couple weeks now, btw.
Anyways, I draw, get good alignment, aim, then form the pressure pocket with my tongue that will become a little mouth grunt. After that all I have to do is focus on expanding by increasing back tension. The tension in your back bleeds into your neck and jaw muscles just a little bit,and it's enough to pop the seal on that pressure pocket. So I basically have a pressure driven clicker that's non mechanical.
It took me a week to find the right tongue position, and it requires good form. If I drop my head and reach for the string it clamps down my jaw, and makes the pop almost impossible to trigger.