If you are carrying a cell phone and it is turned on, then it's possible that someone with the proper equipment is now tracking each and every movement you make. I'm not an expert on this but I'd wager that the people most likely to have the "proper equipment" are employees of the US government. What this means is that the US government may, at this very moment, be monitoring you.
Don't believe me? Then do some research. And after that, maybe you'll want to consider turning your cell phone off if you are every doing something that you don't want the US government to find out about...or heck, if you are just walking down the street and you don't want the government to know about that!