In reply to nickinscottishmountains:
As said above, you have to put a sticky pad onto the helmet that stays there permanently. It won't come off - I've had mine on there some time and its suffered some abuse during climbing and it hasn't come off. I completely trust it.
When the camera is off, the pad is fairly unobtrusive. I forget its there and no one has ever commented on it. It doesn't damage the helmet at all, and it should come with all the bits you need.