To be used with Ion Pumping Cords. The LED will light when the red and black leads on Ion Cords are connected to the red and black leads on the Tester. When the leads are reversed, the LED will not light up. Powered by two 1.5 volt AA or one 9 volt battery (not included). Note: For the Manaka Ion Cords, a dim light may show on the LED when the clips are connected. Red-to-red and black-to-black, the cords are however, still functional, but the battery in the tester is overpowering the sensitive diode.