When drilling holes near sockets or switches, there’s a risk of damaging a wire with the drill. Good news is that there’s an unusual way to help find hidden wires in the wall. Connect a microphone to a tape recorder and start the device to record with maximum volume. Place the microphone near the future hole in the wall. The spots where there are hidden wires will make a low hum from the dynamics of the tape-recorder. It will be safe to drill in the places where there’s no humming sound.