Every operation device that requires power once plugged into a powerline will release electromagnetic radiation, and that radiation can be used to intercept information by various technologies verified by both the U.S. and the USSR (at the time it existed).
These radiations can easily be used to remotely record keystrokes.
According to the Kaspersky Lab:
“Keystrokes can be remotely tracked with high accuracy at the 67-feet (20-meter) distance by using a homemade device that analyzes the radio spectrum and costs around $5,000. It is interesting to note that the attack is equally effective against common cheap USB keyboards, expensive wireless keyboards with a signal encryption, and built-in notebook keyboards. All of the devices work on the same principle and generate electromagnetic noise. The difference is stipulated by the signal power, which depends upon the length of the data transmission wire.”
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