The Pain-Less Pro is a miniature, professional, hand held, FDA approved TENS unit. A TENS unit is a transcutaneous electrical nerve stimulation unit. The electrodes sent electrical currents to your nerves and muscles stimulating them and helping to ease any pain. Most TENS units are safe to use unless your pregnant, have heart conditions, pace makers etc. This is becoming a popular pain management tool and commonly used as an alternative to pain medications that are often harmful and addictive.