A car's navigation system that helps us find our way to any destination and a smartphone that locates a nearby restaurant are among the everyday marvels of life today. But GPS, like any technology, poses perils as well as benefits. If a technology can tell you where you are, it can just as easily tell someone else where you are.
Does the government, for instance, have the right to always know your whereabouts? Most of us would adamantly answer "no," but government lawyers are arguing the opposite in a case under review by the U.S. Supreme Court.
On Tuesday, the court is set to hear arguments in a case involving the surveillance of an alleged drug dealer in which the government claims it has the right to use GPS technology to track anyone's motor vehicle without warrant and without the owner's consent.
The government's argument in U.S. v. Jones relies in great part on a court ruling from the early 1980s, U.S. v. Knotts, in which the use of beeper-tracking technology was deemed not to require a warrant. The new case illustrates how technologies such as GPS have dramatically changed the balance when it comes to "reasonable expectations of privacy," as provided in the Fourth Amendment.
Beeper-based surveillance technologies, which date back to the 1960s, merely enhanced the ability of the police to follow a car. Officers still needed to stay within relatively close range of the vehicle being followed.
GPS technology, by contrast, is a fully automated process. When coupled with wireless communication, it can support broad-scale collection of detailed location information without any human intervention.
With the cost of a GPS chipset down to about $1, it is now technically and economically feasible to track very large numbers of people all the time. Consider what can be surmised about individuals by collecting GPS location data.
Over time, information regarding visits to churches, meeting halls, medical clinics, private residences and bars could reveal people's political and religious affiliation, sexual orientation, faithfulness to their spouse, health or participation in groups such as Alcoholics Anonymous. When the location trails of many individuals are analyzed together, it is even possible to infer social relations between people and much more.
So what about the Fourth Amendment and our "reasonable expectations of privacy"? Do we as a society consider it reasonable for the government to have access to this type of information without warrant and without our consent?
Our research at Carnegie Mellon University shows that, even if we forget about the power of inference afforded by data mining, people still have strong privacy expectations when it comes to disclosing their exact location over extensive periods of time.
We began our investigation of these questions in response to the emergence of sites such as Facebook, as well as the ongoing explosion in smartphone ownership. We were intrigued to see that, while social networking sites such as Facebook have hundreds of millions of users, location-sharing applications such as Google Latitude or Foursquare are still struggling to get past a few million.
Our findings show that this difference in adoption is a direct reflection of people's privacy expectations when it comes to their location. People want to control the conditions under which their location is disclosed, based on who wants to know, where they are or what time of day it is.
Often, they also want to limit the level of detail about their location -- "I'm in town" rather than "I'm at 5000 Forbes Avenue." That's why the locations people disclose to others via Foursquare, called check-ins, are primarily limited to restaurants, concerts and a limited number of other public venues. We do not see too many check-ins at AA meetings or abortion clinics.
Keep in mind that these are the preferences of early adopters of location-based applications. These people are themselves a small minority -- just 5 percent of cell phone users according to a September study by the Pew Research Center. They are among those who express the least concern about their location privacy. Yet even their disclosures are very limited. The majority of us are even more conservative when it comes to disclosing our whereabouts.
If the Supreme Court were to side with the government claim that GPS tracking can be conducted without warrant and without someone's consent, it would effectively adopt an interpretation of people's location privacy expectations that is inconsistent with years of research in this area.
Now more than ever, with the advent of technologies that make large-scale collection and analysis of our activities an economic practicality, the law is our absolute last line of defense. Giving up our "reasonable expectation of privacy" for the sake of expediency would be a grave mistake. It would set a precedent for the large-scale deployment of increasingly invasive technologies, and also suggest to those companies already amassing troves of data about us that privacy no longer matters.
Norman M. Sadeh is director of Carnegie Mellon University's Mobile Commerce Laboratory and co-director of the School of Computer Science's Ph.D. Program in Computation, Organizations and Society ( www.normsadeh.org ). He also signed a friend-of-the-court brief in U.S. v. Jones filed by the Center for Democracy and Technology and the Electronic Frontier Foundation.