Nielsen is turning to Facebook to find out what you’re watching on your mobile device. Starting this fall, Facebook will track the shows its users watch on their phones and tablets and send information about their age and gender to the television ratings company. The arrangement, which begins with the fall TV season, was announced in October 2013 but is getting renewed attention because of the recent controversy over Facebook’s mood experiment.

Historically, Nielsen tracked viewer data by installing meters on TV sets in the homes of about 25,000 households that agreed to participate.

Users will have the chance to opt out of device tracking when they download mobile TV apps — but the opt-out notice may not warn that Nielsen and Facebook are working together.

Unrelated to Nielsen, Facebook caught flak recently over its controversial mood manipulation study.

Those who complain Nielsen ratings don’t reflect true viewing habits may welcome the changes. So will advertisers “clamoring for the data so they can strike the best media buying deals and keep up with the on-the-go consumer who’s increasingly turning to mobile devices for entertainment,” as Ad Week put it.

Privacy advocates aren’t happy. “Consumers really are not aware of the extent to which Facebook is putting their non-Facebook activity to use,” Julia Horwitz, a consumer protections counsel at the Electronic Privacy Information Center, told the Los Angeles Times. “Watching television and surfing the Internet shouldn’t necessarily involve Facebook.”

Cheryl Idell, a Nielsen executive vice president, told the L.A. Times that data gathered from Facebook will be anonymous and aggregated so Nielsen won’t have information about individual users.

“We have worked with Nielsen under strong privacy principles,” a Facebook spokesman told the L.A. Times. “We don’t believe that audience measurement systems should be used to adjust targeting; they should only be used for measurement. This protects the privacy of people viewing ads and ensures that both advertisers and publishers have the same information about the audiences.”

However, as the L.A. Times pointed out, Facebook is obviously interested in online video statistics. This month, the company said it would buy LiveRail, a start-up that specializes in targeted online video ads.

This isn’t the first time Nielsen and Facebook have teamed up. Facebook for years has provided Nielsen demographic data about people who see Internet ads — not just on Facebook but elsewhere.

Nor is Facebook the only social media company Nielsen works with. Last year it joined forces with Twitter to create the “Nielsen Twitter TV Rating,” which tracks what people are tweeting about TV shows. The move brought advertisers to Twitter — and broadcasters because of the power of tweets to improve ratings, especially for reality shows.

Starting this fall, Nielsen will also track household income, family size and education level through a partnership with the marketing arm of Experian, a company better known as a credit reporting agency.

Correction: The original version of this story incorrectly said that the data provided by Facebook would include “where” people were watching a program. That is not the case.