Professor Orin Kerr made an interesting point over at The Volokh Conspiracy: the Supreme Court did not explicitly state that police officers need a warrant to attach a GPS device to a car. On Monday’s post I said that police will need a warrant, but the Court’s decision stops short of stating that. The Court said that the GPS device constituted a “search,” which generally requires a warrant, but there are so many exceptions to that rule that lawyers frequently get them mixed-up.
However, in practicality, the police really will need a warrant. Neither prosecutors nor police officers are going to risk losing otherwise good evidence just to test the state of the law. It may be a few years before the Court resolves this issue definitively.
Natty Shafer Law 
February 2, 2012 at 4:00 PM
That’s an interesting point. I’m curious to see how much weight post-Jones the Katz test will have. To me it seems that Scalia was pretty willing to revert back to the pre-Katz trespass analysis, but Sotomayor emphasized the importance of the Katz test. With a 4-1-4 split, I wonder if Sotomayor’s concurrence will have extra weight.
February 2, 2012 at 4:31 PM
Justice Alito joining the more liberal justices in using of the Katz reasonable expectation of privacy test was a bit surprising. Five justices advocating the continuation of Katz means lower court judges will have some difficulty figuring out which test controls.
February 2, 2012 at 11:56 PM
I tend to agree with you, that this will have the practical effect of causing prosecutors to apply for warrants rather than risk it. Of course, the opinion raised some really important questions.
I find it hard to believe that the prosecutor failed to even mention the automobile exception, the same exception that was invented for the exact reason a GPS device was used – the car is mobile! ?ow can Scalia analyze this case in any other way than he’s analyzed all of the other cases – the Fourth Amendment doesn’t protect against all searches, just unreasonable ones?
Also, what happens if, as they discussed briefly at oral argument, the police attach the GPS to the license plate or other state property? There goes the trespass-based theory of a “search.”
February 3, 2012 at 10:09 AM
That is an interesting question about the license plate. Using 18th century trespass law to decide a Fourth Amendment case is going to lead to muddled situations like that.
What happens if the government attaches a bug to a city-issued trash can? Say a defendant keeps his trash can in his garage 6 days a week until trash day. Is the government allowed to do that because there was no trespass or is the home sacrosanct?