My first instinct is that the signal probably doesn't need to be ultrasound. In the same way that my phone will sometimes hear my car radio and falsely hear, "h

My first instinct is that the signal probably doesn't need to be ultrasound. In the same way that my phone will sometimes hear my car radio and falsely hear, "hello Google", I bet the beacon can just be planted on top of the signal and match filtered to a decent SNR. Similar to image steganography, it doesn't need to be perceptible to the listener. Compression issues would exist, but at least they wouldn't be fighting against the transmission hardware.