There have been some other threads which have contained the advertised radiation exposure by the nude-o-scopes. But I can't recall whether the person in the machine knows when they are getting radiated.

Do the machines have any type of indicator lamp visible when emitting?
What keeps a demented TSA person from hitting the button as many times as they want? Anything? What about a whacko sitting in the booth hitting the button like he's on a Playstation? Is that possible without anyone knowing? Scary, IMO.