GPS Evidence and the Fourth Amendment
Global Positioning System (GPS) is a system of satellites in outer space that provides detailed information about the position and timing of anyone on the Earth. The system is maintained by the United States Government. Anyone with a GPS receiver can track their location to within a few meters or less using the GPS system.
Originally, civilian service for GPS devices was significantly downgraded. However, under the presidency of former President Bill Clinton, civilians began to receive the most accurate GPS service available.
GPS may be accurate to within a few meters. However, accuracy varies on the quality of the receiving device. Some devices may be accurate to within a few centimeters.
As GPS technology has become more widely available, the price of GPS technology has fallen dramatically. Today, GPS technology can be found with the iPhone as well as inexpensive computerized navigation systems for cars.
Since GPS has the power to tell an individual exactly where a tracking device is at any given time, the use of GPS devices has flourished as an investigatory device in many parts of the United States.
Local courts are still grappling with whether the use of a GPS device to track a defendant over a long period of time violates a defendant's right to be free of warrantless searches and seizures.
GPS and the Fourth Amendment
The test for whether a given search or seizure violates the Fourth Amendment is whether the defendant's "reasonable expectation of privacy" has been violated.The defendant, through his or her own actions, may waive their right to protection from warrantless searches: "What a person knowingly exposes to the public ... is not a subject of Fourth Amendment protection" 
Can a police officer walk up to your vehicle and place a GPS monitoring device on your car, tracking your every move for months on end? Until recently, the question was answered with an affirmative. The decisions of these lower courts was based on two U.S. Supreme Court cases: United States v. Knotts, 460 U.S. 276 (1983) and United States v. Karo, 468 U.S. 705 (1984).
In United States v. Knotts, government investigators placed a beeper inside a drum which allowed them to follow the drum to the defendant's home. The court concluded:
A person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another. When [one of the defendant's accomplices] traveled over the public streets he voluntarily conveyed to anyone who wanted to look the fact that he was traveling over particular roads in a particular direction, the fact of whatever stops he made, and the fact of his final destination when he exited from public roads onto private property.
... [N]o ... expectation of privacy extended to the visual observation of [the] automobile arriving on [the private] premises after leaving a public highway, nor to movements of objects such as the drum of chloroform outside the cabin in the "open fields."
Visual surveillance from public places along [the] route or adjoining Knotts' premises would have sufficed to reveal all of these facts to the police.
The court noted that there was no evidence the drum was ever within the defendant's home, where he could have had a higher level of privacy expectation.
In Karo, the Court was faced with a similar situation. However, in Karo the beeper was used to determine the exact location of the GPS unit within a storage facility.
In 2009, the Wisconsin Court was faced with the question of whether the placement of a GPS monitoring device on the defendant's vehicle violated the defendant's Fourth Amendment rights. The court's reasoning was based on Knotts and Karo:
Knotts and Karo teach that, to the extent a tracking device reveals vehicle travel information visible to the general public, and thus obtainable by warrantless visual surveillance, the use of the device does not normally implicate Fourth Amendment protections. It follows that no Fourth Amendment violation occurred here simply because the police used a GPS device to obtain information about the defendant's car that was visible to the general public.
Until 2010, all major U.S. Courts of Appeals who looked at the issue reached the same conclusion. 
However, in August 2010, the United States Court of Appeals for the District of Columbia broke with precedent by concluding that the use of GPS evidence could violate a defendant's Fourth Amendment rights.
In Maynard, the police used a GPS device on the defendant's vehicle 24 hours a day for four weeks. The police did not have a warrant to use the GPS device.
The court rejected the government's contention that Knotts was binding precedent. They distinguished Knotts by concluding that the kind of comprehensive, sustained monitoring that comes from GPS use was of a different nature than the beeper information in Knotts and that the information gleaned from the GPS unit was not in fact "public":
Two considerations persuade us that the information the police discovered in this case the totality of Jones' movements over the course of a month was not exposed to the public: First, unlike one's movements during a single journey, the whole of one's movements over the course of a month is not actually exposed to the public because the probability that anyone will observe all those movements is effectively very low. Second, the whole of one's movements is not exposed even though each individual movement is exposed, because that whole reveals more, sometimes a great deal more, than does the sum of its parts.
The court then looked at the second step, whether the defendant's expectation of privacy was "reasonable.":
A person does not leave his privacy behind when he walks out his front door, however. On the contrary, in Katz the Court clearly stated ?what [one] seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.? 389 U.S. at 351. Or, as this court has said, outside the home, the 'Fourth Amendment ... secur[es] for each individual a private enclave, a zone bounded by the individual's own reasonable expectations of privacy.' Reporters Comm. for Freedom of Press v. AT&T, 593 F.2d 1030, 1042-43 (1978).
The case is likely to be appealed to the United States Supreme Court.
- United States v. Katz, 389 U.S. 347 (1967)
- United States v. Katz, 389 U.S. at 351 (1967)
- State of Wisconsin v. Sveum, 2008AP658-CR (2008)
- United States v. Garcia, 474 F.3d 994 (7th Cir. 2007); United States v. Marquez, 605 F.3d 604 (8th Cir. 2010);United States v. Pineda-Moreno, 591 F.3d 1212 (9th Cir. 2010)
- United States of American v. Maynard, No. 08-3030 (Aug. 6, 2010)