General Tools MSV100 Metal Stud and Voltage Detector 3-in-1 Tester is a great testing solution for a variety of technicians working in residential and contracting fields that can locate behind walls metal cables and pipes, wooden joists and studs, as well as AC voltage for "hot" wires and outlets. The General Tools MSV100 automatically compensates for wall thickness in all 3 measurement modes, has a center arrow display with beeper for pinpointing edges, and features a marking slot on the top of the unit.