As a fan of the The Wire, I can find lots of plot twists and exciting scenes that illustrate the basic constitutional balance between the rights of individuals and the power of law enforcement. The Wire portrays police who follow the rules and those who don't as they wiretap, search, photograph and otherwise conduct their investigations into complex criminal cases.
In one episode, Detective Leander Snydor has followed a drug dealer to a house which might link him to other criminal relationships. Snydor skillfully walks past the dealer's car, fixes a GPS tracking system to the underside of the vehicle, and walks away with a whistle.
That might seem like smart cop work when aimed at an enormous, fictional drug ring in the mean streets of Baltimore. But GPS is no longer HBO fiction. In Madison, Wisconsin, where law enforcement agents used GPS to track someone suspected of violating a restraining order without first getting a warrant, it's very, very real. Unfortunately, according to the Wisconsin Court of Appeals, we should let go of the expectation that police need permission to track our movements.
The Wisconsin Court of Appeals held in State of Wisconsin v. Sveum that the use of a GPS device was not a "search or seizure" and didn't fall under the Fourth Amendment. The consequence of this reasoning is that the police are free to track individuals' vehicular movements wherever they go and without any approval by a court. This is true even though tracking someone's movements can give a detailed picture of someone's personal associations—they can be tracked to churches, bars, protests or their doctor's office.
While a GPS tracking device isn't as invasive as a strip search, we expect the Fourth Amendment to protect us from police spying by making it a requirement that law enforcement agents demonstrate to a court that they have a strong reason to believe that such tracking will turn up evidence of a crime.
On Friday, the ACLU and the Electronic Frontier Foundation (EFF) filed a friend-of-the-court brief (PDF) with the Wisconsin Supreme Court to urge justices to reverse the lower court's decision. While we can all agree that the police should help enforce a restraining order, allowing them the power to obtain information on the location of anyone's car and movements, for any reason or for no reason at all, without a valid warrant, is unconstitutional.
GPS tracking shouldn't be used by police or other government agencies without a judge's agreement that the tracking is based on a good reason to believe it will turn up evidence of a crime. Without court oversight or just cause for the use of this technology, our private lives as revealed by our movements can surely turn our country into a Big Brother reality.
In the brief (PDF), the ACLU and EFF argue that, whether or not the U.S. Constitution applies, the Wisconsin Supreme Court should conclude that Article I, Section 11 of the Wisconsin Constitution protects this state's citizens from such intrusive police surveillance.