In the wake of the attacks on Paris, debate in the United States has again looked determining the appropriate balance between privacy and security, especially with regard to encryption.
Similarly, European politicians have begun discussing the issue with regard to airline passenger data.
New technology permits device cross- by including a unique sound in a TV commercial that a mobile application containing the SilverPush “audio beacon” recognizes. That app would typically be brand-specific. Once the sound is heard, the application knows what the user is watching.
Link: http://www.forbes.com/sites/thomasbrewster/2015/11/16/silverpush-ultrasonic-tracking/