Commentary--You may already know this, but your cell phone happens to be a miniature tracking device that can be used to monitor your location from afar.

There are times when knowing your exact location is useful, of course. It would be handy for a phone to help you find a gas station in a pinch, or bleep when you're about to take the wrong highway exit.

But the FBI and the U.S. Department of Justice have seized on the ability to locate a cellular customer and are using it to track Americans' whereabouts surreptitiously--even when there's no evidence of wrongdoing.

A pair of court decisions in the last few weeks shows that judges are split on whether this is legal. One federal magistrate judge in Wisconsin on Jan. 17 ruled it was unlawful, but another nine days later in Louisiana decided that it was perfectly OK.

This is an unfortunate outcome, not least because it shows that some judges are reluctant to hold federal agents and prosecutors to the letter of the law.

It's also unfortunate because it demonstrates that the FBI swore never to use a 1994 surveillance law to track cellular phones--but then, secretly, went ahead and did it, anyway.

When lobbying for that law, the Communications Assistance for Law Enforcement Act, then-FBI Director Louis Freeh assured the U.S. Senate that location surveillance would never take place unless there was evidence of wrongdoing.

"It does not include any information which might disclose the general location of a mobile facility or service, beyond that associated with the area code or exchange of the facility or service," Freeh testified. "There is no intent whatsoever, with reference to this term, to acquire anything that could properly be called 'tracking' information."

So much for promises from politicians.

Nobody is saying, of course, that police should be denied the ability to locate a felon-on-the-run in an actual emergency. Current law allows agents to do precisely that because there would be ample evidence of wrongdoing, or probable cause, that they can present to a judge.

The problem is that the Justice Department's current official position--a flip-flop from its previous official position--says police should be able to secretly monitor your whereabouts as long as they claim that tracking could possibly be "relevant" to some investigation. Not only is that insufficiently privacy-protective, it doesn't track what the law actually says.

Some judges are courageous enough to point this out. U.S. Magistrate Judge William Callahan in Wisconsin last month denied the Justice Department's request to track a suspected drug user through his Cingular Wireless phone. The feds were helping out on behalf of the Wisconsin narcotics bureau, which claimed in court documents that "by obtaining cell site information for (the target's) cellular telephone, it may be able to determine (his) source for cocaine."

Citing Freeh's testimony, Callahan said it was abundantly clear that "the language which found its way into the law was predicated on the director's assertion to Congress that (the law) would not be used to secure location information for the cellular phone user." But, Callahan noted, prosecutors are relying on "precisely" that language today.

"I cannot find any contemporaneous understanding by either Director Freeh or the Congress that the government had the capability that it now has to ascertain the location of a person using a cell phone," Callahan added.

It's true that in the case before Callahan, prosecutors were asking for the location of Cingular cell towers being used by the cell phone only when calls were being made, not when the handset was idle. That yields only a rough approximation of a location, depending on how many towers there are nearby.

But given the Justice Department's logic, there's nothing stopping prosecutors from asking for more data next time. Thanks to regulations from the Federal Communications Commission, wireless handsets must know their locations within a few hundred feet, regardless of whether their owner wants it. Some newer gadgets, such as the Hewlett-Packard's iPaq hw6515, have built-in GPS (Global Positioning System) receivers that are far more precise.

Those detailed data streams are potentially available to police. In one court document (click here for PDF), U.S. Attorney Michael Garcia claims, "A cell phone user voluntarily transmits a signal to the cell phone company and thereby assumes the risk that the cell phone provider will reveal to law enforcement the cell site information."

Consider the implications. If you voluntarily transmit your exact GPS-derived location to a cellular provider--so you can get information returned about nearby restaurants or driving directions--the Justice Department apparently believes that your location should be available without a warrant.

That's not what Louis Freeh promised, that's not what Congress wrote, and that's not what a majority of federal judges who have looked at this have decided. But for now, there's nothing stopping prosecutors from shopping around and finding a sympathetic judge who will find some way to interpret the law in their favor next time.