| Nowadays a Fluke VoltAlert
Back in the day (15 years ago) i had one i built myself - Basically the "sense" was feeding to the base of a 5-tier Darlington of 2N2222's, and the last one was lighting a Red LED. Two 10MOhm resistors were provided as pull-down on the bases of 2 of the transistors (iirc every 2nd transistor) to pull it down just enough so it won't be lighting all the time
The entire setup, with 2 AAA batteries was assembled into a translucent White Plastic tube from a fax machine paper roll. The battery connection was at the "holding" end of the wand, and provided the capacitive electrode to my hand. A defective electrolitic capacitor, that happened to just fit into the tube and hold in there, was stuffed in from the other end. Not used as a capacitor but just as the "sensing" end electrode, one of the capacitor's leads was connected to the base of the 1st transistor
This tester was WAY more sensitive than any store bought one - it could sense 230V from 2ft on a good day, detect wiring through (cement block !) walls, etc. But it would also light up all the time from interference and static. Walk past it with a block of styrofoam and it would light up
I also have a few simple contact (Neon) testers, and at about the same time i made the non contact one, i also had a contact one which i modded with the glow lamp from a starter (that glows in Purple) instead of the original Neon. Resistor used was something like 1MOhm
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