I've worked with ultrasound on the receiving end on android before, using the built in mic to capture ultrasound data. We never came across a device that was un

I've worked with ultrasound on the receiving end on android before, using the built in mic to capture ultrasound data. We never came across a device that was unable to hear the data, and we tested on what I would consider a pretty large variety of phones. As far as transmitting goes you're probably right though, and seeing as the dash button is the receiver in this scenario it makes sense