ESPN and Fox Sports have signed up for Nielsen's out-of-home viewership ratings that tracks what people watch when they're watching television outside of their homes. 

People in the Nielsen sample carry a device the size of a pager that picks up audio encoding from a nearby television and that tracks when they're watching at a bar, restaurant, hotel, work or a second home.

Fox Sports averaged 35.1 million viewers for last Thanksgiving's game between Dallas and Washington but the out-of-home viewership elevated the total to 48.7 million viewers. That represents a 40 percent increase from its traditional number.

According to ESPN execs, they have seen similar increases when out-of-home audiences were added to its Christmas Day schedule for the NBA.

CBS and NBC are also in discussions for adding the service.

“We are currently working with Nielsen to ensure that its out-of-home methodology accurately reflects the full audience picture,” an NBCUniversal spokesperson said via email.

NFL Network likely will participate in Nielsen’s out-of-home measurement, according to an NFL source.

While NFL ratings fell by 10 percent last season, the increase from out-of-home ratings could change the trajectory of their numbers.