I was in Vegas not too long ago and I came across a booth that offered free 'massages' from these gadgets. I tried it on, no paint at all, and it felt good. I think it send small electrical impulses depending where the pads are put. Is this safe to use? I was a bit skeptic about it. I know that they wouldn't be able to sell it, if it wasn't 'safe', but i'm talking about in the long run?