T.E.N.S. units have been dispensed by doctors to their patients for home use. They operate on a 9v. transistor battery and have small wires and pads that adhere to a painful area and alleviate pain. Tiny free nerve endings secrete a chemical called "substance P" that transmits pain signals to our brain. T.E.N.S. units artificially stimulate free nerve endings, thereby depleting them of substance P, literally stopping the pain signal in its tracks.