Omron Pain Reliever Portable E3 TENS Massager HV-F021-EV Electronic Nerve Stimulator engage TENS (Transcutaneous Electrical Nerve Stimulation) technology, a clinically proven drug-free non-invasive therapy that uses low voltage electrical current to reduce and relieve muscular and neuropathic pain. Designed with 6 pre-set programs for back, shoulders, joints and muscles. It is widely used by physiotherapists and pain specialists. The OMRON TENS unit consists of a simple, portable, battery-powered device that delivers mild electrical impulses through electrodes placed on top of the intact skin near the source of pain and stimulates the underlying nerves, thus easing the pain. TENS therapy session lasts for 15 minutes before it automatically shuts off. There should only be 2 sessions at a time. It should only be used 3 times per day.