[OZ4]

This signal probe looks like it would be real handy for troubleshooting radios. Not only can it find noisy components it can show that the oscillator is running. And there is no electrical connection with the circuit.

This youtube video shows how its built and how it works. The demo starts at about 52 minutes in.
https://www.youtube.com/watch?v=uVkJqqZroN0

And here he uses it again in this video at time 1:16:32
https://www.youtube.com/watch?v=6P4C9at5rV8

[Electrothaumaturgist]

That is totally awesome! Well worth constructing one! 

[jcassity]

this is a must have for so many applications....

[Hudson54]

Absolutely! Constructing one is definitely worth it. It's an awesome endeavor with great rewards.