This circuit was found in a 90s American publication. The same configuration appears in several places on this site, obtained from different sources. The lamps can be replaced by LEDs.
This sensor circuit for currents of the order of nanoamperes was found in an American...
This circuit was obtained from a 1964 magazine and has some interesting features such as the input...
Suggested by a 90’s Radio Electronics, this circuit automatically activates the recording switch of an...