Its main function is an electrical tester. It can test bulbs, fuses, switches, trace wires and find bad grounds. It works on almost all unenergized circuits 3, 6, 12, 24, 110, & 220 AC/DC circuits. It also functions as a flashlight. Your customers can use it on cars, boats, trailers, RVâÄôs, and at home. Its main benefit is that it is so compact; you can carry it with you at all times, a handy belt holster is included in each package. Megatester is compact enough to easily fit in glove boxes, kitchen drawers or purses.