General Tools MSV100 Stud, Metal and Voltage Detector Ideal for building contractors, carpenters, plumbers, HVAC/R specialists, home inspectors, electricians, realtors, home owners and interior decorators Detects wood joists/studs, livewires and pipes/cables behind walls Automatically compensates for wall thickness; in voltage mode, automatically compensates for distance to wire Center arrow and beeper pinpoint edges; marking slot on top of unit Power source is 1 9V battery (included)