This circuit can detect static charges or extremely low voltages. The circuit was found in ancient American documentation and makes use of a JFET. A BF245 which is a more modern transistor can be used.
Indicated in Maxim's documentation from the 90's, this circuit has a gain of 40 dB and an output...
I found this simple circuit in an English magazine from 1984. The circuit can be assembled easily...
This is the receiver circuit for the transmitter of the previous circuit using an integrated...