Transcutaneous electrical nerve stimulators (TENS) The patient may use a TENS unit at home for back pain relief on a long-term basis. TENS units are about the size of a pack of cigarettes and typically cost $250 - $700. All units allow the user to adjust the intensity of the stimulation; some units also allow the user to select high-frequency stimulation (60 - 200 Hz) or low-frequency stimulation (<10 Hz). High frequency stimulation, sometimes called "conventional", is tolerable for hours, but the resultant pain relief lasts for a shorter period of time. Low-frequency stimulation, sometimes called "acupuncture-like", is more uncomfortable and tolerable for only 20-30 minutes, but the resultant pain relief lasts longer. TENS users should experiment with various electrode placements. Electrodes can be placed over the painful area, surrounding the painful area, over the nerve supplying the painful area, or even on the opposite side of the body. TENS users need to try the unit for several days with several electrode placements prior to deciding if it will be useful. A home trial for several days to weeks is preferable.