In United States v. Moore, the Tenth Circuit held that Jester the Drug-Sniffing Canine’s leap into a detainee’s car through an open window after giving an alert but not a final indication did not violate the Fourth Amendment. The alert alone was sufficient to provide probable cause, says the Court (as it has said before). The fact that Jester was wrong---there were no drugs in Mr. Moore's car---did not, apparently, play a role in the Court’s decision.
If you'd like a slightly more skeptical view on alerts and probable cause, check out the Seventh Circuit’s opinion in United States v. Bentley. Mr. Bentley himself did not fare any better than did Mr. Moore, with the Seventh Circuit ultimately holding that an alert by “Lex” provided probable cause for a search of Bentley’s car. But the Court reached that conclusion with considerable reluctance. Lex, it seems, was “at the back of the pack” when it came to reliability. In the field, Lex’s alert rate was 93%, while his accuracy rate was 59.5%. Why the gap between alerts and hits? Probably because Lex’s handler gives Lex a treat---a rubber hose stuffed with a sock!---every time he alerts. As the Seventh Circuit observed, “If Lex is motivated by the reward (behavior one would expect from any dog), he should alert every time. This giftee policy seems like a terrible way to promote accurate detection on the part of a service animal, lending credence to Bentley’s argument that Lex’s alert is more of a pretext for a search than an objective basis for probable cause.” That said, the Court ultimately decided that a 59.5% accuracy rate is good enough for probable cause. But the Court warned that “this should not be a race to the bottom, however. We hope and trust that the criminal justice establishment will work to improve the quality of training and the reliability of the animals they use, and we caution that a failure to do so can lead to suppression of evidence. We will look at all the circumstances in each case, as we must.”