SAN JOSE, Calif. (CBS Sacramento) — When choosing a smart television, buyers are often presented with a variety of features. One they may not be aware of: that TV could be watching you.

Vizio Smart TVs, one of the most popular manufacturers, can track your viewing tendencies and report them to advertisers, as reported by ProPublica.

The feature, “Smart Interactivity,” is already turned on as a default setting for millions of people who have purchased the device. Viewers are able to turn off the setting, that is, if they know it even exists.

“Non-personal identifiable information may be shared with select partners… to permit these companies to make, for example, better-informed decisions regarding content production, programming and advertising,” Vizio said in a statement.

Vizio seems to be taking a new approach by tracking viewers by default, while competitors like San Jose-based Samsung or LG Electronics leave it to customers to turn the setting on. Vizio’s sharing with advertisers also reportedly lets them target devices like your phone, which other companies do not.

Smart Interactivity analyzes watching habits of viewers including content, time, and channel. The patterns are connected to the viewer’s IP address, which can be used to identify other devices in the home.

The company updated its privacy policy to say that it had begun providing watching habits to companies that “may combine this information with other information about devices associated with that IP address,” according to ProPublica.

In an October filing, Vizio said that its new tracking tactics will increase profit margins in the business and will be able to provide “highly specific viewing behavior data on a massive scale with great accuracy.”

Companies like Neustar, Tapad, and Experian have either denied working with the company or said they are unable to share the name of companies they work with.