[ndsipa_pomu]

I wonder if that's feasible in a room filled with many servers and fans going?

[runjake]

Yes, just modulate the fan noise on the transmitter, and apply a filter on the receiver.

[faidit]

Doesn't being able to modulate the fan presume you already control the target device?

[alextingle]

It's possible to get malware onto even air-gapped machines. This is a way to then communicate across the air-gap.