Prompted by the Center for Democracy and Technology (CDT), the Federal Trade Commission has scheduled a workshop to discuss cross-device tracking technologies. Using ultrasonic, inaudible pitches, the technology allows a user’s online behavior to be tracked across phones, TVs, tablets and computers. The pitches can be — and are already — embedded in TV commercials, ads in a computer browser and apps. The consumer is not made aware that the tracking technology has been activated and there is no way to opt out.

According to Ars Technica, when the pitch is played, nearby tablets and smartphones can detect it, and browser cookies pair a single user to multiple devices and “keeps 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.” This ability to easily track activity across devices is new.

“As a person goes about her business, her activity on each device generates different data streams about her preferences and behavior that are siloed in these devices and services that mediate them,” says the CDT. “Cross-device tracking allows marketers to combine these streams by linking them to the same individual, enhancing the granularity of what they know about that person.”

In fact, marketers are able to construct a “shockingly detailed snapshot of the person being tracked.”

SilverPush, Drawbridge, Flurry and Adobe are among the companies working on cross-device tracking. CDT officials are most concerned with the San Francisco-based SilverPush, which links devices via apps using the SilverPush software development kit.

SilverPush says its technology doesn’t listen to all the noises in proximity to devices. The company will not list the apps using its technology, but, as of April 2015, it is embedded in 67 apps monitoring an estimated 18 million smartphones. The company recently received $1.25 million in venture capital.