Electrostatic field detector (MOSFET based)

Hi, guys.

I've read several descriptions of pretty simple device for electrostatic fields detection, based on MOSFET transistor, but i've found no schemes or details and i can't understand how this device actually works. Does anybody heard about it? May be you can give me some explanations, references etc...

I want to discover fields around the human body. Particularly, i have intention to detect acupuncture points with this device.

Thanks in advance!