The New York Court of Appeals today decided People v. Weaver, 12 N.Y.3d 433 (May 12, 2009), holding that the NY Constitution prohibits the use of GPS transmitters on vehicles without a warrant, following other state courts analyzing the issue under their constitutions. This is a stunningly prescient opinion:

At first blush, it would appear that Knotts does not bode well for Mr. Weaver, for in his case, as in Knotts, the surveillance technology was utilized for the purpose of tracking the progress of a vehicle over what may be safely supposed to have been predominantly public roads and, as in Knotts, these movements were at least in theory exposed to "anyone who wanted to look" (id. at 281). This, however, is where the similarity ends.

Knotts involved the use of what we must now, more than a quarter of a century later, recognize to have been a very primitive tracking device. The device was, moreover, used in a focused binary police investigation for the discreet purpose of ascertaining the destination of a particular container of chloroform. And, in this application, during the single trip from the place where the chloroform was purchased to the Knotts cabin, the beeper was fairly described by the Court as having functioned merely as an enhancing adjunct to the surveilling officers’ senses; the officers actively followed the vehicle and used the beeper as a means of maintaining and regaining actual visual contact with it. The technology was, in this context, not unconvincingly analogized by the Court to a searchlight, a marine glass, or a field glass (id. at 283, citing United States v Lee, 274 US 559, 563 [1927]).

Here, we are not presented with the use of a mere beeper to facilitate visual surveillance during a single trip. GPS is a vastly different and exponentially more sophisticated and powerful technology that is easily and cheaply deployed and has virtually unlimited and remarkably precise tracking capability. With the addition of new GPS satellites, the technology is rapidly improving so that any person or object, such as a car, may be tracked with uncanny accuracy to virtually any interior or exterior location, at any time and regardless of atmospheric conditions. Constant, relentless tracking of anything is now not merely possible but entirely practicable, indeed much more practicable than the surveillance conducted in Knotts. GPS is not a mere enhancement of human sensory capacity, it facilitates a new technological perception of the world in which the situation of any object may be followed and exhaustively recorded over, in most cases, a practically unlimited period. The potential for a similar capture of information or "seeing" by law enforcement would require, at a minimum, millions of additional police officers and cameras on every street lamp.

That such a surrogate technological deployment is not -- particularly when placed at the unsupervised discretion of agents of the state "engaged in the often competitive enterprise of ferreting out crime" (Johnson v United States, 333 US 10, 14 [1948]) -- compatible with any reasonable notion of personal privacy or ordered liberty would appear to us obvious. One need only consider what the police may learn, practically effortlessly, from planting a single device. The whole of a person's progress through the world, into both public and private spatial spheres, can be charted and recorded over lengthy periods possibly limited only by the need to change the transmitting unit's batteries. Disclosed in the data retrieved from the transmitting unit, nearly instantaneously with the press of a button on the highly portable receiving unit, will be trips the indisputably private nature of which takes little imagination to conjure: trips to the psychiatrist, the plastic surgeon, the abortion clinic, the AIDS treatment center, the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, synagogue or church, the gay bar and on and on. What the technology yields and records with breathtaking quality and quantity, is a highly detailed profile, not simply of where we go, but by easy inference, of our associations -- political, religious, amicable and amorous, to name only a few -- and of the pattern of our professional and avocational pursuits. When multiple GPS devices are utilized, even more precisely resolved inferences about our activities are possible. And, with GPS becoming an increasingly routine feature in cars and cell phones, it will be possible to tell from the technology with ever increasing precision who we are and are not with, when we are and are not with them, and what we do and do not carry on our persons -- to mention just a few of the highly feasible empirical configurations.

. . .

Technological advances have produced many valuable tools for law enforcement and, as the years go by, the technology available to aid in the detection of criminal conduct will only become more and more sophisticated. Without judicial oversight, the use of these powerful devices presents a significant and, to our minds, unacceptable risk of abuse. Under our State Constitution, in the absence of exigent circumstances, the installation and use of a GPS device to monitor an individual's whereabouts requires a warrant supported by probable cause.

The opinion even quotes Brandeis' 1928 Olmstead dissent on the right to be let alone:

The protection guaranteed by the Amendments [the Fourth and Fifth] is much broader in scope [than the protection of property]. The makers of our Constitution undertook to secure conditions favorable to the pursuit of happiness. They recognized the significance of man's spiritual nature, of his feelings and of his intellect. They knew that only a part of the pain, pleasure and satisfactions of life are to be found in material things. They sought to protect Americans in their beliefs, their thoughts, their emotions and their sensations. They conferred, as against the Government, the right to be let alone -- the most comprehensive of rights and the right most valued by civilized men. To protect that right, every unjustifiable intrusion by the Government upon the privacy of the individual, whatever the means employed, must be deemed a violation of the Fourth Amendment. And the use, as evidence in a criminal proceeding, of facts ascertained by such intrusion must be deemed a violation of the Fifth.