TENS is most commonly delivered from small, hand held, battery powered devices. They can be purchased 'over the counter' in many (but not all) countries. In some locations, they need to be 'prescribed' by a therapist, doctor or other healthcare practitioner. Most multi-modal clinic based stimulators include TENS as an option, though its use in the clinic is less well supported than its use as a home based, patient delivered therapy. Examples of typical TENS units are illustrated below.