"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," said Mark Johnson of Loyalty Marketers Association.
Marketing insider Mark 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.
"It does seem creepy that companies are collecting all this information about consumers," said smartphone user Harrine Freeman.
Harrine Freeman is so creeped out, she turns off her GPS when she drives and shops. She also clears her browser history.
Freeman said, "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.
"This is something that consumers are automatically opted into," said Rainey Reitman of Electronic Frontier Foundation.
Critics say cell phone companies tell customers what data they're collecting by sending them privacy notices 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".
Reitman said, "I don't really think that most people are going to review every e-mail they get from their cell phone company and then go through the extra step of opting out of this targeted advertisement."
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," said Johnson.
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 always press "no".