Hundreds of privacy-invading apps are using ultrasonic sounds to track you

‘A new privacy-busting technique that tracks consumers through the use of ultrasonic tones may have once sounded like the stuff of science fiction novels, but today it’s reality.
These near-silent tones can’t be picked up by the human ear, but there are apps in your phone that are always listening for them. This technology is called ultrasonic cross-device tracking, and it works by emitting high-frequency tones in advertisements and billboards, web pages, and across brick-and-mortar retail outlets or sports stadiums. Apps with access to your phone’s microphone can pick up these tones and build up a profile about what you’ve seen, where, and in some cases even the websites you’ve visited.
The technology is still in its infancy, but it’s growing in popularity.
In the past year, researchers found 234 Android apps that include the ability to listen for ultrasonic tones “without the user’s knowledge,” one paper said.’
Read more: Hundreds of privacy-invading apps are using ultrasonic sounds to track you