A TENS (transcutaneous electrical nerve stimulation) unit is a small, battery-operated device that delivers low-voltage electrical current to provide pain relief. The device consists of electrodes that are placed on the surface of the skin, which are connected to the device by wires. The electrodes are placed at or near nerves where the pain is located or at trigger points. The electrical impulses can reduce the pain signals going to the spinal cord and brain, which may help relieve pain and relax muscles. They may also stimulate the production of endorphins, which are the bodys natural painkillers. TENS is a non-invasive method of pain relief that can be used alone or in addition to prescriptions or over-the-counter pain-relieving medications. It can be used to help with many types of chronic (long-term) pain, such as arthritis, back and neck pain, fibromyalgia, muscle pain, neuropathic pain, and period pain. TENS is most helpful for chronic pain when used for at least 30 minutes while you are active. It is less effective when you are sitting still, lying down, or resting. TENS is generally considered safe, with fewer side effects than some other types of pain relief.