It isn't? "The technology, called ultrasonic cross-device tracking, embeds high-frequency tones that are inaudible to humans in advertisements, web pages, and

It isn't? "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." "any device microphone—like those accessed by an app on a smartphone or tablet—can detect the signal" How is this any different from a bluetooth beacon being detected by a mobile app? You are just broadcasting the identifier in a different manner.