reporter: every time you watch tv, your tv is likely watching you. through that box which collects information on show after show after show. all that data is sent anonymously to advertisers focused on reaching people likely to buy certain products or watch certain shows. what is the benefit to people like me? the benefit to consumers is you get more ads that are relative to you. reporter: john werther helped pioneer advertising on the internet. now he is doing it with tv. if this is done right, how much money is this worth? we think billions of dollars. reporter: why? because what you watch tells a lot about you. sometimes unexpectedly. a rerun of saved by the bell at 9:00 on saturday morning is one of the most