BESTEST Non-contact Voltage Testers quickly sniff out ac voltages, without electrical contact. Light flashes and vibrates when ac voltage is present. Test for ac voltage on outlets, light bulb sockets, extension cords, appliances, power tools, ac motors, light switches and circuit breakers. Identify hot side of ac receptacles plus find and trace electrically live wires or objects inside walls. Determine if metal surfaces are live or ground and detect presence of high-voltage electric fields. Also detects leaks in microwave ovens.