Velleman mains voltage detector kit velleman k7101 the velleman mains voltage detector kit makes it easy to check wires for mains voltage even if they are installed in or behind walls the device can also be used to trace interruptions in wiring a flashing led indicates whether or not voltage is present and the flash speed indicates how close the wire is if an audible signal is also needed space has been provided on the pcb for a buzzer to be connectedvelleman k7101 mains voltage detecto