In reply to Rock_Monk3y:
I was involved in an incident using auto-belays with helmets.
A qualified instructor was running an ad hoc session on a mobile climbing tower (turn up & pay a few £ for some climbs). A kid (maybe 9yrs old) was having a go. He was wearing a helmet and had already done a few up and downs, he got a bit cocky on one descent and was bouncing around a bit, he slipped and went side on to the wall as he descended (rather than feet on wall).
The helmet edge got caught up on a hold and he was left hanging from his helmet strap in some distress, half way up the wall.
Luckily he managed to free himself, just as I was preparing to solo up the wall to 'rescue' him. (Obviously not the safest rescue to attempt but definitely the quickest in this situation). The only injury was a nasty burn on his neck from the strap but could have been a lot worse.
There were a number of 'Learning points' to this incident around the use of such walls, rescue procedures, what holds to fit etc, but the biggest one was around not wearing helmets.
Let me know if you want any more info.