A transcutaneous electrical nerve stimulation unit is an electrical device that sends low-voltage currents into the body. Electrode pads are placed over specific nerves on the body to conduct the currents from the unit to the nerves.ranscutaneous electrical nerve stimulation may result in instant or prolonged pain relief. Through the release of endorphins and the control of nerves, TENS sends relief directly to the site of pain. Some patients experience permanent pain relief after repeated sessions with a TENS unit.