Lightning Detector with Coherer

This is a simple lightning detector that uses a coherer.

When a radio frequency signal is received and its magnitude is great enough to trigger the coherer into conduction, a current flows through transistor that amplifies the current for the counter relay. When the relay takes a step forward, the hammer tap on the coherer's tube. This "knock" returned the metal powder back to their low-conductance state.

https://www.youtube.com/watch?v=lEYOqLs_vWU