The U.S. Federal Trade Commission (FTC) has this week released a warning letter addressed to 12 smartphone app developers regarding an audio monitoring tool which reportedly operates in their software unbeknown to users.

According to the letter [PDF], the undisclosed developers are using software development kits from an Indian firm called SilverPush, which enables apps to ‘listen’ to unique audio codes embedded in television and ad content to establish what TV programmes and adverts are being played in the proximity.

The ‘Unique Audio Beacon’ technology is allegedly configured to gain permissions to the device’s microphone to gather audio data, even while the user is not actively using the application. With this information, SilverPush is able to collect a detailed record of what television and ad content is being viewed by the user to better deliver targeted advertising and analytics.

The letter goes on to explain that while there is no obvious need for the app to require microphone access, it still requests access permission in order to install. Once downloaded, the accused apps do not disclose details of the audio beacon feature – either as part of the setup, in a dedicated privacy policy, or anywhere else.

While SilverPush claims the audio beacon functionality is not currently embedded in commercials airing in the U.S., the FTC explains that if the app allows third-party monitoring of TV-viewing habits, and if the developers state or imply that their products do not collect viewing data when in reality they do, it is in violation of Section 5 of the FTC Act prohibiting unfair and deceptive business practices.

“These apps were capable of listening in the background and collecting information about consumers without notifying them,” Jessica Rich, director at the FTC’s Bureau of Consumer Protection, commented in a statement. “Companies should tell people what information is collected, how it is collected, and who it’s shared with,” she added.