Frustrated woman with mobile device © Jacqueline Veissid, Photodisc, Getty Images

Your cellphone is the enemy.

Sure, it connects you with people, the Internet, stupid games and even your bank account. But it's also a tracking device that your family, your favorite retailer and virtually any law-enforcement agency in the world can use to find you.

And you're complicit in helping them do so. By keeping your phone on, you are letting any number of people have access to private information about you that you might not think you're giving out.

Sometimes you're putting the information into pretty packages by signing into sites like Foursquare -- which is linked to your Facebook account -- when you enter a restaurant, a bar, even a church.

"Location information can reveal a great deal about a person," said Catherine Crump, a staff attorney at the American Civil Liberties Union.

It can show who you're friends with, what medical offices you visit, what organizations you belong to and, in worst-case situations, where you've been when you don't want to be found.

And, just like you see on the TV crime shows, the longer your cell phone is tracked, the more information about you is uncovered.

Consider the uproar around the controversial "Girls Around Me" app for iPhones that looked to some like a stalking tool. The developers, in a long-winded response to The Wall Street Journal in March, said the app was meant only "to make geo-social exploration of popular venues easy and visual."

It did so by using publicly available data from Foursquare and Facebook to tell users which bars and nightclubs, for example, were hot on a particular night.

It was billed as a go-to tool for guys looking for hot chicks who used Foursquare to see where they checked in on a given map area. In fact, the app would note anyone, male or female, who had checked in at places in the vicinity.

Not only would users know who was where but, through public information posted on Facebook pages, the users in some cases were able to find out a girl's name, what she looked like, her birthdate, where she went to school and worked, who she might be with and any number of things that people share through social media sites. What's more, the girls had no idea they were being tracked that way.

(After Foursquare cut off access to the app, the developer pulled it but said it would continue to tweak it and plans to reintroduce it.)

That underscores the conundrum with your cellphone: While it makes it convenient to find your friends, directions or the weather, you give up a little piece of your privacy each time you use it.

"Your cellphone is your best friend who is a tattletale," said Mike Gikas, a senior electronics editor at Consumer Reports. "It's there for you, it comforts you, it gets you stuff -- but then it tells the world about it. And the more you tell it, the more it's going to share," he added.

Police track cellphones

Increasingly, law-enforcement agencies are using cellphones to track the bad guys, but catch a lot of good people like you in the crosshairs, according to an exhaustive study by the ACLU.

The ACLU asked 380 police departments nationwide about their policies and practices for cell-phone tracking, with and without a warrant. Of the 200 that responded, only 10% said they didn't use cell-phone tracking at all.

The report revealed that the majority practiced at least some form of cell-phone tracking, with many doing it "quite frequently."

The rationale, of course, is to ferret out criminals and terrorists by seeing where they go, to whom they talk and what they're texting without the sometimes time-consuming process of first securing a warrant.

GPS tracking by police is also extremely valuable in the case of a missing child, a potential suicide or strong belief that someone is facing immediate danger of death or serious injury.

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