Is your Android phone tracking you?

ABC News' Rebecca Jarvis looks into how much information your cell phone is really collecting about you.
3:55 | 12/07/18

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Transcript for Is your Android phone tracking you?
We want to turn to that "Gma" investigation. Do you know how much information your cell phone is really collecting about you and your location? Our chief business and technology correspondent Rebecca Jarvis tried an eye-opening experiment. Rebecca, this could be more than we actually realize. Yeah, Cecilia, good morning. Nice to see you, so many of us now are carrying a smartphone. It's the top gift this holiday season and this morning we're taking a closer look at the vast amounts of information these devices are collecting on us and then sending back to companies like Google. What if someone or something was tracking your every move? Not just your location on a map but your mode of transportation, even your elevation? More than half of Americans have android phones and might be voluntarily agreeing to more than they realize. So, what data is really being collected when you accept Google's terms of service? These are two new phones. We haven't opened any apps on them, neither has a sim card. We did a demonstration when the weather was warmer to find out. Without connecting either phone to a network or wi-fi we traveled around New York City to see if information was being gathered and how often. From the subway to a bike. Heading out on a bike ride around 11:15 in the morning. Reporter: And finally. Getting into a car. It's about 12:15. We're heading into times square. Reporter: Still not connected to any cellular network I arrived back at ABC and enlist the help of cybersecurity expert Megan stifle, a former director in the national security council at the white house. To see what type of information our phones are collecting which might be sent back to Google. We just connected it to our test station. Reporter: Connecting our phones to wi-fi for the first time a startling discovery. This phone doesn't have a sim card. It wasn't connected to the internet but it still was collecting all of that information. Yes, and using all the sensors in the phone to obtain as much information that it can even though it can't send it anywhere. As soon as I connected to the network it was transmitted back to Google. Yes. Reporter: Tracking my unique device's movement, even identifying the mode of transportation and at times taking ten sensor readings per minute. So at 10:25 assesses you were on a rail vehicle. On the train. Even knew when it was tilting underground. At 11:16 what does it say. On bicycle. It says I was on a bicycle? Yes. Which is what I was doing at 11:16 A.M. Yes, then you got off and maybe you were walking around a little bit later. So at 12:05 what were you doing. It says in-road vehicle. Heading uptown to the office. Right. Reporter: When you agree to their terms of service you are agreeing to some types of data sharing. Users might not realize how extensive it is. This is not something the user necessarily opted into or if they did opt into it it was in a fashion that wasn't consistent with their expectations. Reporter: Google tells us in order to provide basic service like security, notification and app updates smartphones need to communicate with their operating system providers and cellular carriers on a regular basis. Google adds they can view, manage or delete the information associated with their Google accounts at any time. Wow, seeing you on that bike and tracking it is something. This is extremely value information and if you think about it, Google's business model, they make the most of their revenue off of advertising sales and advertising when they know when they can pinpoint where you are and what you're doing, they can actually direct an ad to you so imagine you're in a mall but you're on the second floor of the mall, not the first floor, they can send a push alert to your phone suggesting a store on that second floor instead of the first one because they know you're there. Wow, really good information, all right, thanks, Rebecca. Ginger, over to you.

This transcript has been automatically generated and may not be 100% accurate.

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