[fulldecent2]

Just chiming in to note that "1) if your air-gapped computer has malware that can do this, you've already lost" is a problem specific to this implementation.

Other implementations exist (related work, not in 2.4G band) where it is not necessary to install malware to make measurable transmissions.

For example (shilling) https://fulldecent.github.io/system-bus-radio/ allows to broadcast just by loading a web page. And, importantly, this is an attack vector that is reasonable to execute offline (i.e. connected to a local network with HTTP services, but not the internet).