A team of researchers from the Brunswick Technical University in
Germany has discovered an alarming number of Android applications that
employ ultrasonic tracking beacons to track users and their nearby
Their research paper focused on the technology of ultrasound
cross-device tracking (uXDT) that became very popular in the last three
uXDT is the practice of advertisers hiding ultrasounds in their ads.
When the ad plays on a TV or radio, or some ad code runs on a mobile or
computer, it emits ultrasounds that are picked up by the microphone of
nearby laptops, desktops, tablets or smartphones.
SDKs embedded in apps installed on those devices relay the
beacon back to the online advertiser, who then knows that the user of TV
“x” is also the owner of smartphone “Y” and links their two previous
advertising profiles together, creating a broader picture of the user’s
interests, device portfolio, home, and even family members.