This is a circuit that can produce 6 million gain. As well as detecting general electric noise, this circuit can be used to detect “mains hum,” the presence of your hand without any direct contact, and detect static electricity.  Here is the schematic diagram of the circuit:

6 MILLION GAIN circuit schematic

The mains cable can be located by this circuit by moving it across any wall. The gain is achieved from 200 x 200 x 200. Since the circuit detects very weak electric field, it might look like ghost detector because electric field has weird pattern sometimes. [Circuit’s schematic diagram source: talkingelectronics.com]