Cross-device tracking refers to technology which enables the tracking of users across multiple devices such as smartphones, television sets, smart TVs, and personal computers. More specifically, cross-device tracking is a technique in which technology companies and advertisers deploy trackers, often in the form of unique identifiers, cookies, or even ultrasonic signals, to generate a profile of users across multiple devices, not simply one. For example, one such form of this tracking uses audio beacons, or inaudible sounds, emitted by one device and recognized through the microphone of the other device.