The next time you’re lying on the couch and fiddling with your phone while streaming Stranger Things or watching Mr. Robot, be aware — an app could be recording and tracking your viewing habits, and using the information in conjunction with your location to target you with ads during your next browsing session.

A recent story in the New York Times highlights a data firm called Alphonso that collects television viewing information through a smartphone’s microphone and sells that data to advertisers. The tracking software is piggybacked onto free games and apps such as Beer Pong: Trickshot and Pool 3D. Even when the app is not in use, it can listen for audio cues from TV shows and commercials to monitor what you’re watching.

Although the company claims it doesn’t listen to conversations, according to its website, it uses “advanced fingerprinting technology to identify ads and programming airing on TV in a fraction of a second, in a completely anonymous fashion.” The site calls it a TV Data Cloud and boasts that “40 million smart TVs, set-top boxes, mobile and living room devices with embedded Alphonso technology report viewership data in real time.”

The Times notes that more than 250 games that use Alphonso software can be downloaded from the Google Play store, many of them targeted to children. The CEO maintains that it’s all perfectly legal and consumers can opt out at any time.

Justin Brookman, of the advocacy group Consumers Union, told the Times that the nebulous nature of the opt-in notice doesn’t provide enough detail. “When you see ‘permission for microphone access for ads,’ it may not be clear to a user that, Oh, this means it’s going to be listening to what I do all the time to see if I’m watching Monday Night Football,” he said.

Alphonso relies on the content-recognition company Shazam to identify the excerpts contained in its data cloud, and Shazam then sells the information back to Alphonso, which packages it and sells it to advertisers.

The company said its software is running on about a thousand different apps and games, so it’s quite possible you have one or more of them in your library. To check, go into Settings on your phone and then review the permissions of the app in question. If it has microphone access and the game doesn’t need it, toggle the mic permission off.