While many companies are cleaning up their client databases to comply with the new General Data Protection Regulation a.k.a. GDPR, other companies work equally hard on technologies to bypass such regulations. One of these new technologies is the ultrasonic cookie made possible by, for instance, Google Nearby.

Cookies are tiny files placed on your computer that keep track of your internet behaviour. Since they collect private data laws have been established to control their usage. Over the past years we have got used to websites asking us to allow the use of cookies to “improve our experience” of the website. Because regulatory organisms are always two or more steps behind reality, it is often quite easy to get around the rules they impose.

The ultrasonic cookie is one of these clever tricks to bypass the law. This type of cookie employs the ability of mobile devices to hear and produce audio frequencies beyond the highest frequency typically perceived by humans. By broadcasting short ultrasonic frequency messages and by listening to them, mobile devices can communicate with each other without the user noticing.

Because a smartphone’s microphone is almost always activated, ultrasonic cookies also allow communication between apps installed on the device and broadcasting systems installed in places like shopping malls. As an example, if you happen to have the Acme Gadget Superstore app installed on your phone and Acme Gadget Superstore uses ultrasonic cookies, they can follow you around in the store and present personalised advertisements.

Luckily, there are always people trying to combat evil and so you can install for free the SoniControl app developed by a team of researchers from the St. Pölten University of Applied Sciences in Austria. This open-source app creates an ultrasonic firewall on your phone effectively blocking ultrasonic cookies.