I was thinking about this too. If it's possible to send out arbitrary frequencies with it you could have a one way channel even if the air gapped machine doesn'

I was thinking about this too. If it's possible to send out arbitrary frequencies with it you could have a one way channel even if the air gapped machine doesn't have a mic. Only the receiver would need one. The air gapped machine would just be transmitting 24/7 hoping another machine is in range.