543 U.S. 405 (2005)
Illinois State Trooper Daniel Gillette stopped respondent Roy Caballes for speeding on an interstate highway.1 When Gillette radioed the police dispatcher to report the stop, a second trooper, Craig Graham, a member of the Illinois State Police Drug Interdiction Team, overheard the transmission and immediately headed for the scene with his narcotics-detection dog.2
When they arrived, respondent's car was on the shoulder of the road and respondent was in Gillette's vehicle.3 While Gillette was in the process of writing a warning ticket, Graham walked his dog around respondent's car.4 The dog alerted at the trunk.5 Based on that alert, the officers searched the trunk, found marijuana, and arrested respondent.6 The entire incident lasted less than 10 minutes.7
Respondent was convicted of a narcotics offense and sentenced to 12 years' imprisonment and a $256,136 fine.8 The trial judge denied his motion to suppress the seized evidence and to quash his arrest.9 Although the Appellate Court affirmed, the Illinois Supreme Court reversed, concluding that the canine sniff unjustifiably enlarged the scope of the traffic stop.10
The Supreme Court granted certiorari on a narrow question concerning the canine sniff during the traffic stop. The Court proceeded on the assumption that the officer conducting the dog sniff had no information about respondent except that he had been stopped for speeding.11
Whether the Fourth Amendment requires reasonable, articulable suspicion to justify using a drug-detection dog to sniff a vehicle during a legitimate traffic stop?12
Official conduct that does not compromise any legitimate interest in privacy is not a search subject to the Fourth Amendment.13 Governmental conduct that only reveals the possession of contraband compromises no legitimate privacy interest.14 This is because the expectation that possession of contraband will not come to the attention of the authorities is not the same as an interest in privacy that society is prepared to consider reasonable.15 A canine sniff by a well-trained narcotics-detection dog is sui generis because it discloses only the presence or absence of narcotics, a contraband item.16
No. The initial seizure of Caballes when he was stopped on the highway was based on probable cause and was concededly lawful.17 The duration of the stop was entirely justified by the traffic offense and the ordinary inquiries incident to such a stop.18 The dog sniff was performed on the exterior of Caballes's car while he was lawfully seized for a traffic violation.19 The sniff revealed no information other than the location of a substance that no individual has any right to possess.20
Because the dog sniff did not infringe Caballes's constitutionally protected interest in privacy, it did not change the character of the lawful traffic stop into an unlawful seizure.21
The Fourth Amendment does not require reasonable, articulable suspicion to justify using a drug-detection dog to sniff a vehicle during a legitimate traffic stop.22
Related opinions on this issue
Justice Souter dissented on the ground that the assumption underlying Place that trained sniffing dogs do not err is untenable given substantial evidence of canine error rates arising from handler mistakes, dog limitations, and currency contamination.23 Once fallibility is acknowledged, a positive alert does not necessarily indicate contraband and the sniff instead functions as a limited search that reveals undisclosed facts about private spaces, requiring Fourth Amendment scrutiny under the Terry framework.24 Because the only basis for the stop was speeding and no independent suspicion of drugs existed, the sniff search was unreasonable and its fruits should be suppressed.25
Joined by Justice Souter
Justice Ginsburg, joined by Justice Souter, dissented on the ground that the canine sniff impermissibly expanded the scope of the initially valid traffic stop beyond what Terry permits.26 The second Terry inquiry requires that the investigation remain reasonably related in scope to the circumstances justifying the initial interference, yet introducing the drug dog converted the encounter into a broader, more adversarial drug investigation without any cause to suspect narcotics.27 This approach exposes law-abiding motorists to routine, suspicionless drug sweeps and undermines Fourth Amendment protections by allowing every traffic stop to become an occasion for calling in detector dogs.28