Dystopian corporate surveillance threats today come at us from all directions. Companies offer “always-on” devices that listen for our voice commands, and marketers follow us around the web to create personalized user profiles so they can (maybe) show us ads we’ll actually click. Now marketers have been experimenting with combining those web-based and audio approaches to track consumers in another disturbingly science fictional way: with audio signals your phone can hear, but you can’t. And though you probably have no idea that dog whistle marketing is going on, researchers are already offering ways to protect yourself.
The technology, called ultrasonic cross-device tracking, embeds high-frequency tones that are inaudible to humans in advertisements, web pages, and even physical locations like retail stores. These ultrasound “beacons” emit their audio sequences with speakers, and almost any device microphone—like those accessed by an app on a smartphone or tablet—can detect the signal and start to put together a picture of what ads you’ve seen, what sites you’ve perused, and even where you’ve been. Now that you’re sufficiently concerned, the good news is that at the Black Hat Europe security conference on Thursday, a group based at University of California, Santa Barbara will present an Android patch and a Chrome extension that give consumers more control over the transmission and receipt of ultrasonic pitches on their devices.
Beyond the abstract creep factor of ultrasonic tracking, the larger worry about the technology is that it requires giving an app the ability to listen to everything around you, says Vasilios Mavroudis, a privacy and security researcher at University College London who worked on the research being presented at Black Hat. “The bad thing is that if you’re a company that wants to provide ultrasound tracking there is no other way to do it currently, you have to use the microphone,” says Mavroudis. “So you will be what we call ‘over-privileged,’ because you don’t need access to audible sounds but you have to get them.”