Reader Trailrunner7 writes: The Federal Trade Commission is warning dozens of developers about some code they've included in their apps that can surreptitiously listen to unique audio signals from TVs in the background and build detailed profiles of what consumers are watching. The technology, produced by a company called SilverPush, is used to track users across devices and the FTC warned the developers that if they don't disclose the use of the code to consumers, they could be violating the FTC Act. The commission sent the letter to 12 app developers whose apps are in the Google Play Store, and warned them that not disclosing the use of SilverPush's Unique Audio Beacon could be a problem. "For example, the code is configured to access the device's microphone to collect audio information even when the application is not in use. Moreover, your application requires permission to access the mobile device's microphone prior to install, despite no evident functionality in the application that would require such access," the letter says.