In United States v. Place, 462 U.S. 696, 709-10, 103 S. Ct. 2637, 77 L. Ed. 2d 110 (1983), DEA agents at LaGuardia Airport in New York, acting on information received from law enforcement officers at Miami International Airport, seized the defendant's luggage after his arrival from Miami and detained it for 90 minutes while they awaited the arrival of a narcotics detection dog. Id. at 698-99. The Court held that "the length of the detention of respondent's luggage alone precludes the conclusion that the seizure was reasonable in the absence of probable cause." Id. at 709. But as the Court later explained in Sharpe when it rejected a per se time limitation for a Terry-stop, "the rationale underlying that conclusion in Place was premised on the fact that the police knew of respondent's arrival time for several hours beforehand, and the Court assumed that the police could have arranged for a trained narcotics dog in advance and thus avoided the necessity of holding respondent's luggage for 90 minutes." 470 U.S. at 684-85. Although acknowledging that "if an investigative stop continues indefinitely, at some point it can no longer be justified as an investigative stop," id. at 685, the Court stated: In assessing whether a detention is too long in duration to be justified as an investigative stop, we consider it appropriate to examine whether the police diligently pursued a means of investigation that was likely to confirm or dispel their suspicions quickly, during which time it was necessary to detain the defendant. A court making this assessment should take care to consider whether the police are acting in a swiftly developing situation, and in such cases the court should not indulge in unrealistic second-guessing. Id. at 686. In United States v. Place, the Court held that exposing a defendant's luggage, located in a public place, to a sniff by a narcotics dog "did not constitute a 'search' within the meaning of the Fourth Amendment." There, the Court reasoned: A "canine sniff" by a well-trained narcotics detection dog . . . does not require opening the luggage. It does not expose noncontraband items that otherwise would remain hidden from public view . . . . Thus, the manner in which information is obtained through this investigative technique is much less intrusive than a typical search. Moreover, the sniff discloses only the presence or absence of narcotics, a contraband item . . . . In these respects, the canine sniff is sui generis. We are aware of no other investigative procedure that is so limited both in the manner in which the information is obtained and in the content of the information revealed by the procedure. Id. In short, the Court has consistently characterized the canine sniff as a unique, minimally invasive species of search that, at least when applied to sniffs of lawfully detained vehicles and luggage in public places, is not a constitutionally relevant intrusion. In this case, we must determine whether the same is true when that unique species of search occurs at the threshold of, and collects information from inside, a private residence.