A Transcutaneous Electrical Nerve Stimulation (TENS) device is typically used to interrupt nerve signals in the body that are causing muscles to spasm. People with conditions such as back pain, migraine headaches, arthritis, knee pain, amputations, shoulder pain, surgery recovery, or cancer might use TENS devices for pain management. The TENS device usually is a pocket-sized, battery-operated unit that a doctor may prescribe to control pain. The U.S. Food and Drug Administration (FDA) has approved the TENS unit as a safe and effective method to help people who are suffering from chronic pain. TENS devices may make it possible for some people to have relief from chronic pain without the use of addicting medicines.