umm... I don't think they do, Deceiver. Haha... we would have heard about something like that by now. If you are trying to learn proper squat depth, use a box and practice squatting.
Yes there would. Someone would always cry about it. Instead of their friends telling them "the judges robbed you," it would be 'this damn thing isn't working right.'
There is a place that makes those things I believe I saw it in a BFS magazine one time. I was wondering about it when I asked questions about squat depth myself. I think it'd be a great thing if you CAN use it in comps but you can't so it wouldn't be a good idea to train with one. BUT website is