The US Federal Trade Commission has told 12 Android app developers to declare their use of an embedded tracker that uses a phone's microphone to detect inaudible sounds in TV ads.
In a letter to the unnamed developers, the regulator warns that failing to let consumers know when an app contains a cross-device tracker from Indian firm SilverPush could violate the FTC Act.
"This functionality is designed to run silently in the background, even while the user is not actively using the application," the FTC tells the developers in question.
"Using this technology, SilverPush could generate a detailed log of the television content viewed while a user's mobile phone was turned on.
