According to officials, 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 Center for Democracy and Technology wrote in recently filed comments to the Federal Trade Commission. The FTC has scheduled a workshop on Monday to discuss the technology. Often, people use as many as five connected devices throughout a given day—a phone, computer, tablet, wearable health device, and an RFID-enabled access fob. Until now, there hasn’t been an easy way to track activity on one and tie it to another. “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,” CDT officials wrote. “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.” The companies,according to officials which are involved are namely SilverPush, Drawbridge, and Flurry These are working on ways to pair a given user to specific devices. Adobe is developing similar technologies. Without a doubt, the most concerning of the companies the CDT mentioned is San Francisco-based SilverPush. CDT officials wrote: The CDT letter also mentioned that cross-device tracking has been put to use by more than a dozen marketing companies. 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. The user is unaware of the audio beacon, but if a smart device has an app on it that uses the SilverPush software development kit, the software on the app will be listening for the audio beacon and once the beacon is detected, devices are immediately recognized as being used by the same individual. SilverPush states that the company is not listening in the background to all of the noises occurring in proximity to the device. The only factor that hinders the receipt of an audio beacon by a device is distance and there is no way for the user to opt-out of this form of cross-device tracking. SilverPush’s company policy is to not “divulge the names of the apps the technology is embedded,” meaning that users have no knowledge of which apps are using this technology and no way to opt-out of this practice. As of April of 2015, SilverPush’s software is used by 67 apps and the company monitors 18 million smartphones. While technology is evolving day by day, corresponding concerns are also increasing. Now when Cross Device Tracking has made its way into the structure of modern online lifestyle, it is very difficult to say what consequences this may offer. As there is no way for someone to detect that they are being tracked. Even if they do manage to detect, there is no way to opt out.