Illinois v. Caballes (dog sniffing reaffirmed)
What I find interesting about the case is the way the majority distinguishes Kyllo v. United States (the use of a thermal-imaging device to detect the growth of marijuana in a home constituted an unlawful search):
Critical to that decision was the fact that the device was capable of detecting lawful activity -- in that case, intimate details in a home, such as "at what hour each night the lady of the house takes her daily sauna and bath." The legitimate expectation that information about perfectly lawful activity will remain private is categorically distinguishable from respondent's hopes or expectations concerning the nondetection of contraband in the trunk of his car. A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment.Since detection of unlawful activity does nto offend the Fourth Amendment, it seems that the issue is overinclusion. But Justice Stevens doesn't speak to the risk of the dog sniffing out lawful, private activity. He states elsewhere in the opinion that the record contains no evidence of high error rates, but doesn't acknowledge that a finding of high error rates, particularly the existence of false positives, would make this case harder to distinguish.
This may be exaggerating the issue, however, since thermal imaging is able to detect 100% of much legal, private conduct, whereas even the highest evidence pegs narcotics dogs error rates as significantly lower.
But I wonder what error percentage would be enough for members of the majority to concede a fourth amendment violation. Kyllo was 5-4 with an interesting majority makeup (Scalia, Souter, Thomas, Ginsburg, and Breyer). So for Scalia, Thomas, and Breyer, the point at which the the search violates the fourth amendment is somewhere between dog-sniffing (12.5-60% according to the dissent) and thermal-imaging (presumably 100%).
UPDATE: Orin Kerr at the Volokh Conspiracy discusses the case
UPDATE: More analysis and links to other blogs on Grits for Breakfast