Simple Electric Field Detector

http://www.reocities.com/CapeCanaveral/Lab/5185/circuit.html#ELECTRIC

The circuit will come handy when you have to follow the mains wires buried in the wall or even water pipes provided they are not too far away (2-4cm max). It will also detect a conversation on a telephone cable without actually touching it (for testing purposes only) and it works as a microphone if you keep a plastic kitchen foil between the probe tip and your mouth. The probe is just the 12mm long gate lead of the transistor. The 33M resistor should be cut short and soldered where the lead enters the transistor case. Connection to the other part of the circuit is via a standard coaxial cable of any length.

The input is not protected and a pair of low leakage diodes (JPAD5) could be connected back to back between gate and ground. I did not find them necessary: I covered, with a small piece of plastic sponge, the probe tip to avoid direct contact with electrified surfaces and used a minimum of care when handling the probe. http://www.reocities.com/CapeCanaveral/Lab/5185/circuit.html#ELECTRIC