Dan Goodin, Ars Technica:
The ultrasonic pitches are embedded into TV commercials or are played when a user encounters an ad displayed in a computer browser. While the sound can’t be heard by the human ear, nearby tablets and smartphones can detect it. When they do, browser cookies can now pair a single user to multiple devices and keep track of what TV commercials the person sees, how long the person watches the ads, and whether the person acts on the ads by doing a Web search or buying a product. […]
The technology, which is typically not disclosed and can’t be opted out of, makes it possible for marketers to assemble a shockingly detailed snapshot of the person being tracked.
Here’s a good test: if a new product or service is something which won’t gather any traction by allowing users to opt-in, it’s probably a privacy nightmare. That it remains a mystery to adtech firms why we find this intrusive and unlikable shows just how out of touch they are.