NEW YORK - September 16, 2010 - Smart phones do many things these days: surf the Internet, send e-mail, take photos and video, and send and receive calls. But one thing they can do that phone companies don't advertise is spy on you.

As long as you don't leave home without your phone, that handy gadget keeps a record of everywhere you go - a record the government can then get from your telephone company.

The law is unclear about how easy it should be for the government to get its hands on this locational data - which can reveal whether you've been going to church, attending a Tea Party rally, spending the night at a date's house, or visiting a cancer-treatment center. A federal appeals court ruled last week that in some cases the government may need a search warrant.

While that's a step forward, it's not good enough. The rule should be that the government always needs a warrant to access your cell-phone records and obtain data about where you have been.

When you carry a cell phone, it is constantly sending signals about where you are. It "pings" nearby cell-phone towers about every seven seconds so it can be ready to make and receive calls. When it does, the phone is also telling the company that owns the towers where you are at that moment - data the company then stores away indefinitely.

There is also a second kind of locational data that phone companies have, thanks to a GPS chip that is embedded in most smart phones now. This is even more accurate - unlike the towers, which can only pinpoint a general area where you may be, GPS can often reveal exactly where you are at any given moment within a matter of a few feet.

There are some good reasons for this, which is why the government is actually forcing the phone companies to do a better job of knowing where you are.

In the name of improving emergency services, the Federal Communications Commission will require phone companies to meet benchmarks in 2012 for how closely they can pinpoint a caller's location.

"About 90% of Amerikans are walking around with a portable tracking device all the time, and they have no idea," says Christopher Calabrese, a lawyer with the American Civil Liberties Union's Washington office.