If you're willing to use a typewriter you're willing to use a computer with no network connection, so all you need to do is block radio transmissions. A faraday cage can't cost that much compared to the other costs involved in espionage.

People can hop airgapped networks using speakers and microphones.

I had a discussion with a friend about The Thing[1], an invention by Léon Theremin and how ingenious it was that it required no external power source and can be turned on/off at will by transmitting at a certain frequency. The trouble with this is that it's still possible to identify the retransmission. In fact, this was how it was discovered.

What if the room had a length of surgical or other type of long tubing embedded into the wall so that the detector was a fair distance away? Essentially, a very crude stethoscope originating in a wall outlet or other place in the room that already has an orifice(s) and terminating at another location with a passive resonator.

By decoupling the transmitter from the audio source by using a non-electronic medium, it's possible to still eavesdrop on keystrokes even in an em-shielded room.

[1] https://en.wikipedia.org/wiki/Thing_(listening_device)

> block radio transmissions

To what attack are you referring here?

TEMPEST

https://en.wikipedia.org/wiki/Tempest_(codename)