I don't know because I haven't asked, but it is the most incredible machine that I have ever tried before. I had to put my feet in water for one of them. I had to put a thing on my head for another. It was rather impressive because they could tell me what I had for breakfast with that thing on my head. I have hung little things on my ears and hooked wires to batteries. I have put my feet on copper plates. With this one I just hold onto a couple of pipes and I can adjust the power of the zap to my own liking. I like it strong enough to make my hands curl up.