These are handy for basic acupoint electromassage, but please use carefully! TENS/EMS machines are not normally recommended for use above the neck. They come in pairs but please don't use both together to send a signal through the brain! The new microcurrent technology only is acceptable for this purpose.
Best setup for TENS/EMS is to put one in an ear and connect it to a pad on the back of the neck. Use only under a physician's recommendation. Each electrode may need to be trimmed down or specifically shaped to fit any particular individual. (Don't trim away the hole for connecting to the pins on the leadwires however)