A similar mind-blown moment for me was reading about foreign intelligence agencies listening for radio frequencies emitted by typewriter keys. They were able to

A similar mind-blown moment for me was reading about foreign intelligence agencies listening for radio frequencies emitted by typewriter keys. They were able to map specific frequencies to specific letters, and could reconstruct most outgoing letters. It inspired a side-project using an SDR (software defined radio) to fingerprint specific hardware I had around the house.