In this paper, we explore the capabilities, the current
prevalence and technical limitations of this new tracking technique
based on three commercial tracking solutions.<p>To this
end, we develop detection approaches for ultrasonic beacons
and Android applications capable of processing these. Our
findings confirm our privacy concerns:<p>We spot ultrasonic
beacons in various web media content and detect signals in
4 of 35 stores in two European cities that are used for location
tracking.<p>While we do not find ultrasonic beacons in TV
streams from 7 countries, we spot 234 Android applications
that are constantly listening for ultrasonic beacons in the
background without the user’s knowledge.