Not unheard of, there was a paper about doing keylogging through the tiny EM fluctuations from a computer's power supply for example: https://ieeexplore.ieee.org/document/10197022

Or data exfiltration through fan noise (60 bits/min): https://www.sciencedirect.com/science/article/abs/pii/S01674...

Or data transfer between computers using only speakers: https://arxiv.org/abs/1803.03422

The list goes on.