City of Indianapolis v. Edmond
In City of Indianapolis v. Edmond, 531 U.S. 32 (2000), the U.S. Supreme Court upheld a dog sniff of a car conducted without any individualized suspicion. Police officers set up a traffic checkpoint to interdict unlawful drugs, and dog sniffs were performed on cars stopped at the checkpoint. Id. at 35. The Court held that the checkpoint constituted a seizure under the Fourth Amendment, which the Court ultimately held to be unconstitutional because not accompanied by some measure of individualized suspicion. Id. at 41.
The Court expressly rejected the argument that the dog sniff was a search subject to Fourth Amendment standards. To the contrary, the Court held that "the fact that officers walk a narcotics-detection dog around the exterior of each car ... does not transform the seizure into a search." Id. at 40. That is because "an exterior sniff of an automobile does not require entry into the car and is not designed to disclose any information other than the presence or absence of narcotics." Id.