Dispatches from the Creation Wars

Appeals Court Gets One Right

Finally, some good news on the 4th Amendment front. A federal appeals court has ruled that the police cannot plant a GPS device on your car and track your movements without a warrant. You can see the full ruling here.

Police cannot surreptitiously stick a GPS unit on your car and track your movements without a warrant, the US Court of Appeals for the District of Columbia has ruled. In an opinion published Friday, the court said that police use of GPS evidence to convict two individuals was a violation of the Fourth Amendment, and that people have a reasonable expectation of privacy when it comes to their movements over an extended period of time.


One would think that this would be an obvious and uncontroversial ruling, but as Orin Kerr, a 4th Amendment expert, points out, it actually seems to conflict with Supreme Court precedent.

n my view, Supreme Court precedent is pretty clear here: It is not a Fourth Amendment search under United States v. Knotts, 460 U.S. 276 (1983), which held that the use of a “beeper” device to monitor the location of a car on public roads — a beepter being “a radio transmitter, usually battery operated, which emits periodic signals that can be picked up by a radio receiver” — is not a search. Knotts held:

A person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another. When [the defendant] 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.

In my view, the reasoning of Knotts applies to the use of a single GPS device to determine a person’s public location. That wouldn’t apply for use of a location device in a home or private place, as the Court held the year after Knotts in United States v. Karo. And I agree that as matter of policy, we might want a privacy statute to limit what the Fourth Amendment does not. But the Supreme Court’s statement, “A person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another” — seems to apply in the same way regardless of whether the device used to determine those movements is a beeper or a GPS device.

Kerr interprets the ruling to establish a “mosaic” theory of the 4th amendment. He describes this as “whether government conduct is a search is measured not by whether a particular individual act is a search, but rather whether an entire course of conduct, viewed collectively, amounts to a search. That is, individual acts that on their own are not searches, when committed in some particular combinations, become searches. Thus in Maynard, the court does not look at individual recordings of data from the GPS device and ask whether they are searches. Instead, the court looks at the entirety of surveillance over a one-month period and views it as one single “thing.”

Kerr is not convinced by the ruling, and I’m not convinced necessarily by this particular line of reasoning, but as one of those “libertarian-minded readers” he mentions, I think at least the conclusion is correct. And I think the precedent in Knotts is wrong as well.

Certainly the police have the authority to track your movements by following you and doing active surveillance. They have the same right to ride the roads as you do. But planting a device on your car is an entirely different thing. Planting a device on your vehicle means violating your property rights in a way that following you obviously does not.

This clearly implicates the Fourth Amendment’s guarantee to be secure in your “persons, houses, papers, and effects.” They can no more plant a bug in your car than they can in your house, and they can no more track your movements by vehicle than they can attach a homing device to your body. Certainly not without a warrant. We cannot allow technology to give the government easy access to information they would have had to violate the constitution to access previously.