The 7th Circuit Court of Appeals ruled last week that police can place a GPS tracking unit on a suspect's car without obtaining a search warrant. In US v Garcia (2007 U.S. App. LEXIS 2272), decided Feb. 2, Judge Richard Posner found that such a device was a mere "augmentation" of police officers' natural ability to follow a car.

In the Garcia case, an informant alerted police that Garcia used meth with her and said he intended to resume producing meth; he was also taped on a security camera buying chemicals to make meth. The police found his car and attached a GPS tracking device. When they retrieved the device, they discovered that he had visited a large tract of land. They obtained consent from the owner to search the land and found a meth lab. As they were searching, Garcia drove up. They searched his car and found additional evidence against him.

Following a suspect's car is not a search, since a driver is putting himself in public view. In US v Knotts (460 US 276), police worked with a vendor to replace one of the vendor's chemical drums with one the police owned and into which they had installed a beeper. The Supreme Court held it was legal for the police to "augment" their ability to follow the suspect's car with the beeper.

A person travelling in an automobile on public thorougfares has no reasonable expectation of privacy ... Nothing in the Fourth Amendment prohibit[s] the police from augmenting the sensory faculties bestowed upon them at birth with such enhancement as science and technology afforded them ...

Relying on Knotts, the 7th Circuit held that the GPS unit was similar to the beeper - a mere augmentation of police ability to "tail" a car.

... [I]f police follow a car around, or observe its route by means of cameras mounted on lampposts or of satellite imaging as in Google Earth, there is no search. Well, but the tracking in this case by satellite. Instead of transmitting images, the satellite transmitted geophysical coordinates. The only difference is that in the imaging case nothing touches the vehicle, while in the case at hand the tracking device does. But it is a distinction without any practical difference.

There is a practical difference lurking here, however. It is the difference between, on the one hand, police trying to follow a car in their own car, and, on the other hand, using cameras (whether mounted on lampposts or in satellites) or GPS devices. In other words, it is the difference between the old technology -- the technology of the internal combustion engine -- and newer technologies ... But GPS tracking is on the same side of the divide with the surveillance cameras and the satellite imaging, and if what they do is not searching in Fourth Amendment terms, neither is GPS tracking.

Even so, Judge Posner writes, technological advancements like GPS make it all too easy for police to do wholesale surveillance of citizens.

One can imagine the police affixing GPS tracking devices to thousands of cars at random, recovering the devices, and using digital search techniques to identify suspicious driving patterns. One can even imagine a law requiring all new cars to come equipped with the device so that the government can keep track of all vehicular movement in the United States.

None of this, under Posner's analysis, would constitute a search, although it would be an outrageous invasion of privacy. But the Fourth Amendment protects us against search, not observation of our public doings.

Personally, I think GPS tracking does cross the line. In Knotts, the police used the beeper to help them follow the suspect in their car. It "augmented" their ability to visually track the suspect, so if they lost him in traffic, they could pick him up again.

There was no "following" here at all in the Knotts sense. They simply implanted a spying device and later retrieved the device and its data. This is not observation or tailing. This is obtaining information about one's comings and goings. The police have no "faculties bestowed upon them at birth" to discover at a glance all of the travels of a suspect. To my mind that's a search - distinguished from Knotts - and a warrant should be required.