I love reading the air gap transmission stuff all the time, but something the casual viewer probably won't pick up on, is that both devices have to already have a virus on it.

This does not gain you the initial foothold in the hacker methodology.

This is useful for the post exploitation phase.

This or similar sidechannel is the reason why Trezor One wallet has these weird lines around the PIN pad. This way, the same number of pixels are lit in each line, making it harder to guess the random arrangement of numbers from emissions.

Image credit: https://www.hedgewithcrypto.com/trezor-model-one-review/