Cell phone companies know it, and based on what you do with that phone, they know a lot more about you too. Every time you download an app, search for a web site, send a text, take a picture of a QR code, or drive past a store with your GPS on, your every move may be tracked.  By whom?  Your cell phone company.  

Mark Johnson, Loyalty Marketers Association says, "They know you were playing angry birds. They know that you drove by sears. They know you drove by dominos pizza, so they can take that and take a very unique algorithm that can focus on your behavior. It's very impactful."

Johnson confirms your data trail is worth big bucks to cell phone companies.  Many people have no idea this information is being collected, packaged with details about your age and gender, aggregated and sometimes sold to third parties.   

Harrine Freeman, smart phone user says, "It does seem creepy that companies are collecting all this information about consumers."

Freeman turns off her GPS when she drives and shops. She also clears her browser history.  

"I think it's an invasion of privacy. I don't think cell phone companies should sell your information."

All the major cell phone carriers admit to collecting your info. Verizon acknowledges it aggregates the information, and sells it to businesses without personally identifying users. The Cell Phone Trade Association would not agree to be interviewed on camera, but some cellular companies say there's an advantage here: you get ads that are relevant and can save you money.  

Rainey Reitman, with Electronic Frontier Foundation says, "This is something that consumers are automatically opted into." 

Critics say cell phone companies tell customers what data they're collecting by sending them privacy notices like these that may be difficult to understand and written in fine print.   And they don't like that consumers who don't want to be tracked have to make the extra effort to "opt out".

"I don't really think that most people are going to review every email they get form their cell phone company and then go through the extra step of opting out of this targeted advertisement," Reitman says.

To see what your cell phone carrier is monitoring-log onto its website and read its privacy policy.  Johnson says be sure to read any updates your carrier sends, too, because this tracking technology keeps changing.  

"The amount of data these cell phone companies have has grown tremendously over the last three to four years. With the rapid rise and proliferation of cell phones it will only continue to grow," Johnson says. 

Privacy experts say also be careful of third party apps you download that request to "use your location" if you don't want to be tracked.