The U.S. Supreme Court in a unanimous but somewhat contentious decision (pdf) ruled yesterday that secretly planting Global Positioning-System (GPS) devices on a suspect's vehicle without a court order violated the suspect's Fourth Amendment right against unreasonable searches.
The Fourth Amendment of the U.S. Constitution proclaims:
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
I have blogged about the privacy issues involved in these types of government-sponsored searches several times (for example, Police Use of GPS Without a Warrant: Legal or Illegal? and Police Use of GPS Without a Warrant Ruled Illegal by Federal Court), and there have been a couple of IEEE Spectrum podcasts on the subject as well (see The Car as Informant and GPS Tracking Without a Warrant).
The constitutional issue involved has been confused because some courts, at both the state (e.g., the Wisconsin State District 4 Court of Appeals) and federal (e.g., a district court in Missouri just last month) have ruled previously that police putting GPS trackers on suspects' vehicles was legal, while others, including the New York State Court of Appeals, have said such activity was not. The court cases where GPS tracking was ruled legal will now have to be reassessed.
What makes yesterday's Supreme Court ruling still confusing and increases the likelihood of another case related to the tracking of suspects by electronic means being argued before it, is that five of the court members—Justices Scalia, Roberts, Kennedy, Thomas, and Sotomayor—concurred under one line of reasoning (Justice Sotomayor filed a separate concurring opinion), while the other four, Justices Alito, Ginsburg, Breyer, and Kagan, concurred using a different line. Each group said the other needed to rethink its arguments. (Interestingly, the split was not down "party" lines; Sotomayor does not often vote with the first four justices named nor does Alito with the last three.)
According to a story at CNN—and the 34-page opinion, which I encourage you to wade through—the five justices led by Scalia reasoned that the government, by placing a surveillance device on a suspect's vehicle, was committing an illegal trespass under the Fourth Amendment, i.e., the Government was obtaining "information by physically intruding on a constitutionally protected area." Because the government's trespass was clearly involved, the information gained from the secretly placed GPS system was not admissible in court.
That said, the five justices' opinion did acknowledge that what's left up for future constitutional debate was whether getting the same information from other electronic sources without having to resort to physical trespass was legal or not. Their opinion said that it may be legal for the government to keep visual track of a suspect in public places for as long as it likes and has the resources to devote to such an activity. However, the government "achieving the same result through electronic means, without an accompanying trespass [may be] an unconstitutional invasion of privacy," but the justices - with an apparent sigh of relief—stated that "the present case does not require us to answer that question."
The other four justices agreed to disagree with their colleagues using the idea of illegal trespass as the basis for their opinion, and didn't like their kicking the electronic surveillance privacy can down the road. Justice Alito, writing for this group, made their collective annoyance very clear by writing that:
"This holding, in my judgment, is unwise. It strains the language of the Fourth Amendment; it has little if any support in current Fourth Amendment case law; and it is highly artificial."
As summarized in the CNN story, Alito argued that Scalia et al. "...did not address larger legal concerns of searches in the digital age, including GPS. [Alito] said the court should have used this case to clarify the limits of police monitoring of wireless personal communication devices like mobile phones and Internet use."
Alito et al. looked at the issue from what one might call a more "what does the public believe a reasonable expectation to privacy to mean" perspective. In Justice Alito's words:
"I would analyze the question presented in this case by asking whether respondent’s reasonable expectations of privacy were violated by the long-term monitoring of the movements of the vehicle he drove."
Their opinion pointed out that before improvements in surveillance technology, the government would not have even attempted to track a low-level suspect for weeks at a time because of the cost and manpower required. This created a privacy expectation in the public's mind. Now, however, the technology to conduct electronic tracking is ubiquitous and inexpensive. Does this technological capability mean, as some in government have argued, that the public now has to change its notion of privacy? This group of justices aren't so sure.
The Supreme Court may soon have another case with which to attack this issue which is being reviewed in the U.S. District Court of Arizona involving the government's use of "stingray" cell phone tracking devices.
All the justices did seem to agree, however, that Congress needs to get involved in defining what reasonable expectations of privacy and unreasonable searches mean in the electronic age, and the sooner the better.