You can sense electric fields very easily with a Mosfet. All you need is a 2N7000 mosfet, two 1N4005 diodes, one 1 meg trimmer, one resistor and led.
Above are two sensors. One uses a 2N7000 (toward the right), the other is with a power mosfet I happen to have.
Youtube video:
http://www.youtube.com/watch?v=-5EaU2RqtVA
Schematic:
fieldsenser.pdf
Credits:
Based on a circuit by Wilf Rigter
