The California Online Privacy Protection Act (CalOPPA) requires operators of some commercial websites to disclose whether they respond to “Web browser ‘do not track’ signals or other mechanisms that provide consumer the ability to exercise choice regarding the collection of personally identifiable information about an individual consumer’s online activities over time and across third-party Web sites or online services.”

“Do Not Track” refers to an effort, which began in 2009, to create a standard signal which could be broadcast by any web browser, and read by any web publisher, to signal an individual’s preference not to be tracked online. The World Wide Web Consortium (W3C), which develops open standards for use on the internet, created a working group to help standardize a “Do Not Track” or “DNT” signal. The Working group disbanded in 2019, citing insufficient support and adoption of the signal. Some web browsers still permit users to broadcast a DNT signal or “header” which contains one of three values: