TENS equipment. View of transcutaneous electrical nerve stimulation (TENS) equipment, used for painkilling. This portable device is used to relieve pain if analgesic drugs (painkillers) are not working well enough. The main TENS unit (at centre) is powered by a battery (at centre left). The electrodes (at lower right and lower centre) are placed on skin once it has been covered in a gel (at upper right), which aids conductivity. The TENS unit delivers minute electrical impulses through the electrodes. These pulses are thought to stop pain messages from reaching the brain.