Reminds me of the scene in Cryptonomicon where Waterhouse makes a microphone mounted on a safe to crack it.
Hunh. I had seen that done with razor blades and pencil-leads, but never with the leads-alone. Approximately-ten-year-old-me was fascinated by how that worked. Probably more so than by the no-battery-required crystal radio, which he* still considers to be more akin to magic.
* non-ten-year-old me
Here’s a viddy about making that Cryptonomicon mic:
So, a viral ad for headphones. BTW, this is essentially how carbon granule microphones worked in old telephone sets. I used to have to test them - there was a spec on how to move them prior to testing to shake up the granules to make them work correctly. http://en.wikipedia.org/wiki/Carbon_microphone
Many things will modulate voltage or current with applied mechanical forces. It can be quite a bitch if you need to eliminate those effects, whether in precision instrumentation or because of security.
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