Ultrasonic cross-device tracking is a way of tracking people’s behaviour by accessing the microphones in gadgets that people own. The technique works by applications using device microphones (which they have been given permission to access) to track the emission of high-frequency tones (undetectable to humans) in media (such as film/TV, advertisements, and internet pages) or even in popularly frequented locations (such as which shops or entertainment venues they may go to). The signals allow the trackers to keep a record of what media people spend time with, or the locations that they tend to spend time at. By building up these profiles, trackers are able to create increasingly detailed understanding of the user.

This method helps with more detailed tracking especially due to the fact that the profiles can continue to be built up by their gadgets even when they are not connected to the internet, with the records then sent on when a later connection is made. This allows trackers access to much more details than other tracking techniques (such as internet browser trackers) which are limited to only following user’s internet browsing habits.

Additional Information

  • The best way to guard against this technique is to limit the number of apps which are allowed to access a device’s microphone.


Last updated: 1 March 2018