I am more curious about if the phone has to be always listening and what happens if there is noise in the environment.
Also what if the attacker manages to bring a recording device close enough? Is the distance important because of the amplitude or because of the delay due to the speed of sound?
Then there's an error in the linked article, which reads:
"... [it works] by playing an ultrasonic frequency from the mobile device. The system on the computer or any other device analyses the frequency for identification..."
here at 2:15 : http://www.youtube.com/watch?v=X5I6qV2b5iw
I am more curious about if the phone has to be always listening and what happens if there is noise in the environment.
Also what if the attacker manages to bring a recording device close enough? Is the distance important because of the amplitude or because of the delay due to the speed of sound?