Nearly a year ago, vk2zay posted a video on electrets. In it, he also shared a design for a pretty fun electroscope.
As a part of learning KiCAD earlier this year, I turned it into a PCB.
This is the latest result:
The exposed copper area accepts a combination of kapton+sticky copper tape+kapton for some rudimentary shielding. LEDs are 3mm, or 0805 (imperial). The antennae are simply stripped breadboarding wire.
It triggers on things I would have never expected.. like the clear plastic bags some components come in (from a very popular electronics vendor in the middle of nowhere). With the right LEDs (non-diffused/surface mount), people shuffling by light it up, and many are curious enough to pick it up and play with it/ask questions.
You can get your own copy of the PCB through the OSHPark shared project page, or grab the source KiCAD files/Bill of Materials/Placement here. If you want the Gerbers used in fabrication, OSHPark has started exposing those as well, here.