That's basically what Google Nearby uses - one of it's options is to signal to near devices over ultrasonic audio. In fact it looks they are even using it for a

That's basically what Google Nearby uses - one of it's options is to signal to near devices over ultrasonic audio. In fact it looks they are even using it for a payment system http://www.dailymail.co.uk/sciencetech/article-4896748/Google-Tez-payment-app-uses-ultrasonic-sound.html http://www.dailymail.co.uk/sciencetech/article-4896748/Googl... Not sure what the actual technical specification for the method is.