Simple chat program using near ultrasonic frequencies. Works without Wifi or Bluetooth and won't show up in a pcap.So basically there is 2 scripts send.py and listen.py. You can send ASCII messages, send.py transforms it into (near) ultrasonic sound and listener transforms it back into ASCII message.
With MacBook Pro native speakers it didn't work. But with microlab external speakers works pretty well (sender on the left and listener on the right):
Software does not have any practical profit (and the distance between sender and listener is limited by speakers volume and microphone sensitivity), but it very interesting to play with it.