Some years ago I tried the FM transmitter via GPIO hack for the raspberry pi. The range was surprisingly high, around 100m. First google result. https://linuxhint.com/turn-raspberry-pi-fm-transmitter/
https://en.wikipedia.org/wiki/Sensitive_compartmented_inform...
They know it's important to limit what kind of emissions make it from your equipment to the outside world because they've successfully used exactly these techniques in the past to extract information from others.
I'm pretty sure passwords are not shown to reduce shoulder surfing, especially from across the room.
If you want to steal a password, all the cool kids use a microphone or your phone's accelerometers.
https://arxiv.org/abs/1609.09359
https://www.cise.ufl.edu/~traynor/papers/marq-ccs11.pdf
https://phys.org/news/2017-04-criminals-pin-tracking-motion....
> A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen.
https://en.wikipedia.org/wiki/Cathode-ray_tube
That causes a bit more signal than a keyboard, mic, or MEMS accelerometer, eh? :)