在這篇看到現在已經有跨裝置的追蹤機制：「Beware of ads that use inaudible sound to link your phone, TV, tablet, and PC」。
電視廣告利用超高頻 (人類聽不到) 與手機或平板裝置上的應用程式配對，進而組合使用者的行為：
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.
難以被關閉的追蹤機制，看起來就是 NSA、FBI、CIA 之類超愛的技術。