Level 12
New air-gap jumper covertly transmits data in hard-drive sounds:

Researchers have devised a new way to siphon data out of an infected computer even when it has been physically disconnected from the Internet to prevent the leakage of sensitive information it stores...

The method has been dubbed "DiskFiltration" by its creators because it uses acoustic signals emitted from the hard drive of the air-gapped computer being targeted. It works by manipulating the movements of the hard drive's actuator, which is the mechanical arm that accesses specific parts of disk platter so heads attached to the actuator can read or write data. By using so-called seek operations that move the actuator in very specific ways, it can generate sounds that transfer passwords, cryptographic keys, and other sensitive data stored on the computer to a nearby microphone. The technique has a range of six feet and a speed of 180 bits per minute, fast enough to steal a 4096-bit key in about 25 minutes.

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Level 7
This reminds me of a story doing the rounds in the Cold War years.

It was claimed that text could be intercepted from a known make of typewriter using sensitive
microphones to record the clatter of the keys ( even for " golf-ball " type machines )

Very difficult to know if it was true of course !