Florida v. Jardines

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The State points to our decisions holding that the subjective intent of the officer is irrelevant. See Ashcroft v. al-Kidd, 563 U. S. ___ (2011); Whren v. United States, 517

U. S. 806 (1996). But those cases merely hold that a stop or search that is objectively reasonable is not vitiated by the fact that the officer’s real reason for making the stop or search has nothing to do with the validating reason. Thus, the defendant will not be heard to complain that although he was speeding the officer’s real reason for the stop was racial harassment. See id., at 810, 813. Here, however, the question before the court is precisely whether the officer’s conduct was an objectively reasonable search. As we have described, that depends upon whether the officers had an implied license to enter the porch, which in turn depends upon the purpose for which they entered. Here, their behavior objectively reveals a purpose to conduct a search, which is not what anyone would think he had license to do.

 

III

 

The State argues that investigation by a forensic narcotics dog by definition cannot implicate any legitimate privacy interest. The State cites for authority our decisions in United States v. Place, 462 U. S. 696 (1983), United States v. Jacobsen, 466 U. S. 109 (1984), and Illinois v. Caballes, 543 U. S. 405 (2005), which held, respectively, that canine inspection of luggage in an airport, chemical testing of a substance that had fallen from a parcel in transit, and canine inspection of an automobile during a lawful traffic stop, do not violate the “reasonable expectation of privacy” described in Katz.

Just last Term, we considered an argument much like this. Jones held that tracking an automobile’s whereabouts using a physically-mounted GPS receiver is a Fourth Amendment search. The Government argued that the Katz standard “show[ed] that no search occurred,” as the defendant had “no ‘reasonable expectation of privacy’” in his whereabouts on the public roads, Jones, 565 U. S., at ___ (slip op., at 5)—a proposition with at least as much support in our case law as the one the State marshals here. See, e.g., United States v. Knotts, 460 U. S. 276, 278 (1983). But because the GPS receiver had been physically mounted on the defendant’s automobile (thus intruding on his “effects”), we held that tracking the vehicle’s movements was a search: a person’s “Fourth Amendment rights do not rise or fall with the Katz formulation.” Jones, supra, at ___ (slip op., at 5). The Katz reasonable expectations test “has been added to, not substituted for,” the traditional property-based understanding of the Fourth Amendment, and so is unnecessary to consider when the government gains evidence by physically intruding on constitutionally protected areas. Jones, supra, at ___ (slip op., at 8).

 

Thus, we need not decide whether the officers’ investigation of Jardines’ home violated his expectation of privacy under Katz. One virtue of the Fourth Amendment’s property-rights baseline is that it keeps easy cases easy. That the officers learned what they learned only by physically intruding on Jardines’ property to gather evidence is enough to establish that a search occurred.

 

For a related reason we find irrelevant the State’s argument (echoed by the dissent) that forensic dogs have been commonly used by police for centuries. This argument is apparently directed to our holding in Kyllo v. United States, 533 U. S. 27 (2001), that surveillance of the home is a search where “the Government uses a device that is not in general public use” to “explore details of the home that would previously have been unknowable without physical intrusion.” Id., at 40 (emphasis added). But the implication of that statement (inclusio unius est exclusio alterius) is that when the government uses a physical intrusion to explore details of the home (including its curtilage), the antiquity of the tools that they bring along is irrelevant.

 

* * * The government’s use of trained police dogs to investigate the home and its immediate surroundings is a“ search” within the meaning of the Fourth Amendment. The judgment of the Supreme Court of Florida is therefore affirmed.

It is so ordered.

 

JUSTICE KAGAN, with whom JUSTICE GINSBURG and JUSTICE SOTOMAYOR join, concurring.

 

For me, a simple analogy clinches this case—and does so on privacy as well as property grounds. A stranger comes to the front door of your home carrying super-high powered binoculars. See ante, at 7, n. 3. He doesn’t knock or say hello. Instead, he stands on the porch and uses the binoculars to peer through your windows, into your home’s furthest corners. It doesn’t take long (the binoculars are really very fine): In just a couple of minutes, his uncommon behavior allows him to learn details of your life you disclose to no one. Has your “visitor” trespassed on your property, exceeding the license you have granted to members of the public to, say, drop off the mail or distribute campaign flyers? Yes, he has. And has he also invaded your “reasonable expectation of privacy,” by nosing into intimacies you sensibly thought protected from disclosure? Katz v. United States, 389 U. S. 347, 360 (1967) (Harlan, J., concurring). Yes, of course, he has done that too.

 

That case is this case in every way that matters. Here, police officers came to Joelis Jardines’ door with a supersensitive instrument, which they deployed to detect things inside that they could not perceive unassisted. The equipment they used was animal, not mineral. But contra the dissent, see post, at 2 (opinion of ALITO, J.) (noting the ubiquity of dogs in American households), that is of no significance in determining whether a search occurred. Detective Bartelt’s dog was not your neighbor’s pet, come to your porch on a leisurely stroll. As this Court discussed earlier this Term, drug-detection dogs are highly trained tools of law enforcement, geared to respond in distinctive ways to specific scents so as to convey clear and reliable information to their human partners. See Florida v. Harris, 568 U. S. ___ (2013) (slip op. at 2–3, 7–8). They are to the poodle down the street as high-powered binoculars are to a piece of plain glass. Like the binoculars, a drug-detection dog is a specialized device for discovering objects not in plain view (or plain smell). And as in the hypothetical above, that device was aimed here at a home—the most private and inviolate (or so we expect) of all the places and things the Fourth Amendment protects. Was this activity a trespass? Yes, as the Court holds today. Was it also an invasion of privacy? Yes, that as well.

 

The Court today treats this case under a property rubric; I write separately to note that I could just as happily have decided it by looking to Jardines’ privacy interests. A decision along those lines would have looked . . . well, much like this one. It would have talked about “ ‘the right of a man to retreat into his own home and there be free from unreasonable governmental intrusion.’” Ante, at 4 (quoting Silverman v. United States, 365 U. S. 505, 511 (1961)). It would have insisted on maintaining the “practical value” of that right by preventing police officers from standing in an adjacent space and “trawl[ing] for evidence with impunity.” Ante, at 4. It would have explained that “‘privacy expectations are most heightened’” in the home and the surrounding area. Ante, at 4–5 (quoting California v. Ciraolo, 476 U. S. 207, 213 (1986)). And it would have determined that police officers invade those shared expectations when they use trained canine assistants to reveal within the confines of a home what they could not otherwise have found there. See ante, at 6–7, and nn. 2–3.

 

It is not surprising that in a case involving a search of a home, property concepts and privacy concepts should so align. The law of property “naturally enough influence[s]” our “shared social expectations” of what places should be free from governmental incursions. Georgia v. Randolph, 547 U. S. 103, 111 (2006); see Rakas v. Illinois, 439 U. S. 128, 143, n. 12 (1978). And so the sentiment “my home is my own,” while originating in property law, now also denotes a common understanding—extending even beyond that law’s formal protections—about an especially private sphere. Jardines’ home was his property; it was also his most intimate and familiar space. The analysis proceeding from each of those facts, as today’s decision reveals, runs mostly along the same path.

 

I can think of only one divergence: If we had decided this case on privacy grounds, we would have realized that Kyllo v. United States, 533 U. S. 27 (2001), already resolved it.1 The Kyllo Court held that police officers conducted a search when they used a thermal-imaging device to detect heat emanating from a private home, even though they committed no trespass. Highlighting our intention to draw both a “firm” and a “bright” line at “the entrance to the house,” id., at 40, we announced the following rule:

“Where, as here, the Government uses a device that is not in general public use, to explore details of the home that would previously have been unknowable without physical intrusion, the surveillance is a ‘search’ and is presumptively unreasonable without a warrant.” Ibid.

 

1. The dissent claims, alternatively, that Illinois v. Caballes, 543 U. S. 405, 409–410 (2005), controls this case (or nearly does). See post, at 9, 11. But Caballes concerned a drug-detection dog’s sniff of an automobile during a traffic stop. See also Florida v. Harris, 568 U. S. ___ (2013). And we have held, over and over again, that people’s expectations of privacy are much lower in their cars than in their homes. See, e.g., Arizona v. Gant, 556 U. S. 332, 345 (2009); Wyoming v. Houghton, 526 U. S. 295, 303 (1999); New York v. Class, 475 U. S. 106, 115 (1986); Cardwell v. Lewis, 417 U. S. 583, 590–591 (1974) (plurality opinion).

That “firm” and “bright” rule governs this case: The police officers here conducted a search because they used a “device . . . not in general public use” (a trained drug detection dog) to “explore details of the home” (the presence of certain substances) that they would not otherwise have discovered without entering the premises.

 

And again, the dissent’s argument that the device is just a dog cannot change the equation. As Kyllo made clear, the “sense-enhancing” tool at issue may be “crude” or “sophisticated,” may be old or new (drug-detection dogs actually go back not “12,000 years” or “centuries,” post, at 2, 8, 12, but only a few decades), may be either smaller or bigger than a breadbox; still, “at least where (as here)” the device is not “in general public use,” training it on a home violates our “minimal expectation of privacy”—an expectation “that exists, and that is acknowledged to be reasonable.” 533 U. S., at 34, 36.2 That does not mean the device is off-limits, as the dissent implies, see post, at 11–12; it just means police officers cannot use it to examine a home without a warrant or exigent circumstance. See Brigham City v. Stuart, 547 U. S. 398, 403–404 (2006) (describing exigencies allowing the warrantless search of a home).

 

 2The dissent’s other principal reason for concluding that no violation of privacy occurred in this case—that police officers themselves might detect an aroma wafting from a house—works no better. If officers can smell drugs coming from a house, they can use that information; a human sniff is not a search, we can all agree. But it does not follow that a person loses his expectation of privacy in the many scents within his home that (his own nose capably tells him) are not usually detectible by humans standing outside. And indeed, Kyllo already decided as much. In response to an identical argument from the dissent in that case, see 533 U. S., at 43 (Stevens, J., dissenting) (noting that human scan sometimes detect “heat emanating from a building”), the Kyllo Court stated: “The dissent’s comparison of the thermal imaging to various circumstances in which outside observers might be able to perceive, without technology, the heat of the home . . . is quite irrelevant. The fact that equivalent information could sometimes be obtained by other means does not make lawful the use of means that violate the Fourth Amendment. . . . In any event, [at the time in question,] no outside observer could have discerned the relative heat of Kyllo’s home without thermal imaging.” Id., at 35, n. 2.

 

 

With these further thoughts, suggesting that a focus on Jardines’ privacy interests would make an “easy cas[e] easy” twice over, ante, at 9, I join the Court’s opinion in full.

JUSTICE ALITO, with whom THE CHIEF JUSTICE, JUS-TICE KENNEDY, and JUSTICE BREYER join, dissenting.

 

The Court’s decision in this important Fourth Amendment case is based on a putative rule of trespass law that is nowhere to be found in the annals of Anglo-American jurisprudence.

The law of trespass generally gives members of the public a license to use a walkway to approach the front door of a house and to remain there for a brief time. This license is not limited to persons who intend to speak to an occupant or who actually do so. (Mail carriers and persons delivering packages and flyers are examples of individuals who may lawfully approach a front door without intending to converse.) Nor is the license restricted to categories of visitors whom an occupant of the dwelling is likely to welcome; as the Court acknowledges, this license applies even to “solicitors, hawkers and peddlers of all kinds.” Ante, at 6 (internal quotation marks omitted). And the license even extends to police officers who wish to gather evidence against an occupant (by asking potentially incriminating questions).

 

According to the Court, however, the police officer in this case, Detective Bartelt, committed a trespass because he was accompanied during his otherwise lawful visit to the front door of respondent’s house by his dog, Franky. Where is the authority evidencing such a rule? Dogs have been domesticated for about 12,000 years;1 they were ubiquitous in both this country and Britain at the time of the adoption of the Fourth Amendment;2 and their acute sense of smell has been used in law enforcement for centuries.3 Yet the Court has been unable to find a single case—from the United States or any other common-law nation—that supports the rule on which its decision is based. Thus, trespass law provides no support for the Court’s holding today.

 

The Court’s decision is also inconsistent with the reasonable-expectations-of-privacy test that the Court adopted in Katz v. United States, 389 U. S. 347 (1967). A reasonable person understands that odors emanating from a house may be detected from locations that are open to the public, and a reasonable person will not count on the strength of those odors remaining within the range that, while detectible by a dog, cannot be smelled by a human.

 

For these reasons, I would hold that no search within the meaning of the Fourth Amendment took place in this case, and I would reverse the decision below.

 

I

 

The opinion of the Court may leave a reader with the mistaken impression that Detective Bartelt and Franky remained on respondent’s property for a prolonged period of time and conducted a far-flung exploration of the front yard. See ante, at 4 (“trawl for evidence with impunity”), 7 (“marching his bloodhound into the garden”). But that is not what happened.

Detective Bartelt and Franky approached the front door via the driveway and a paved path—the route that any visitor would customarily use4—and Franky was on the kind of leash that any dog owner might employ.5 As Franky approached the door, he started to track an airborne odor. He held his head high and began “bracketing” the area (pacing back and forth) in order to determine the strongest source of the smell. App. 95–96. Detective Bartelt knew “the minute [he] observed” this behavior that Franky had detected drugs. Id., at 95. Upon locating the odor’s strongest source, Franky sat at the base of the front door, and at this point, Detective Bartelt and Franky immediately returned to their patrol car. Id., at 98.

 

1. See, e.g., Sloane, Dogs in War, Police Work and on Patrol, 46 J.Crim. L., C. & P. S. 385 (1955–1956) (hereinafter Sloane).

2. M. Derr, A Dog’s History of America 68–92 (2004); K. Olsen, Daily Life in 18th-Century England 32–33 (1999).

3Sloane 388–389.

 

A critical fact that the Court omits is that, as respondent’s counsel explained at oral argument, this entire process—walking down the driveway and front path to the front door, waiting for Franky to find the strongest source of the odor, and walking back to the car—took approximately a minute or two. Tr. of Oral Arg. 57–58. Thus, the amount of time that Franky and the detective remained at the front porch was even less. The Court also fails to mention that, while Detective Bartelt apparently did not personally smell the odor of marijuana coming from the house, another officer who subsequently stood on the front porch, Detective Pedraja, did notice that smell and was able to identify it. App. 81.

 

II

The Court concludes that the conduct in this case was a search because Detective Bartelt exceeded the boundaries of the license to approach the house that is recognized by the law of trespass, but the Court’s interpretation of the scope of that license is unfounded.

4. See App. 94; App. to Brief for Respondent 1A (depiction of respondent’s home). 5. The Court notes that Franky was on a 6-foot leash, but such a leash is standard equipment for ordinary dog owners. See, e.g., J. Stregowski, Four Dog Leash Varieties, http://dogs.about.com/od/ toys supplies/tp/Dog-Leashes.htm (all Internet materials as visited Mar.21, 2013, and available in Clerk of Court’s case file).

 

 

A

 

It is said that members of the public may lawfully proceed along a walkway leading to the front door of a house because custom grants them a license to do so. Breard v. Alexandria, 341 U. S. 622, 626 (1951); Lakin v. Ames, 64 Mass. 198, 220 (1852); J. Bishop, Commentaries on the Non-Contract Law §823, p. 378 (1889). This rule encompasses categories of visitors whom most homeowners almost certainly wish to allow to approach their front doors—friends, relatives, mail carriers, persons making deliveries. But it also reaches categories of visitors who are less universally welcome—“solicitors,” “hawkers,” “peddlers,” and the like. The law might attempt to draw fine lines between categories of welcome and unwelcome visitors, distinguishing, for example, between tolerable and intolerable door-to-door peddlers (Girl Scouts selling cookies versus adults selling aluminum siding) or be- tween police officers on agreeable and disagreeable missions (gathering information about a bothersome neighbor versus asking potentially incriminating questions). But the law of trespass has not attempted such a difficult taxonomy. See Desnick v. American Broadcasting Cos., 44 F. 3d 1345, 1351 (CA7 1995) (“[C]onsent to an entry is often given legal effect even though the entrant has intentions that if known to the owner of the property would cause him for perfectly understandable and generally ethical or at least lawful reasons to revoke his consent”); cf. Skinner v. Ogallala Public School Dist., 262 Neb. 387, 402, 631 N. W. 2d 510, 525 (2001) (“[I]n order to determine if a business invitation is implied, the inquiry is not a subjective assessment of why the visitor chose to visit the premises in a particular instance”); Crown Cork & Seal Co. v. Kane, 213 Md. 152, 159, 131 A. 2d 470, 473–474 (1957) (noting that “there are many cases in which an invitation has been implied from circumstances, such as custom,” and that this test is “objective in that it stresses custom and the appearance of things” as opposed to “the undisclosed intention of the visitor”).

 

Of course, this license has certain spatial and temporal limits. A visitor must stick to the path that is typically used to approach a front door, such as a paved walkway. A visitor cannot traipse through the garden, meander into the backyard, or take other circuitous detours that veer from the pathway that a visitor would customarily use. See, e.g., Robinson v. Virginia, 47 Va. App. 533, 549–550, 625 S. E. 2d 651, 659 (2006) (en banc); United States v. Wells, 648 F. 3d 671, 679–680 (CA8 2011) (police exceeded scope of their implied invitation when they bypassed the front door and proceeded directly to the back yard); State v. Harris, 919 S. W. 2d 619, 624 (Tenn. Crim. App. 1995) (“Any substantial and unreasonable departure from an area where the public is impliedly invited exceeds the scope of the implied invitation . . . ” (internal quotation marks and brackets omitted)); 1 W. LaFave, Search and Seizure §2.3(c), p. 578 (2004) (hereinafter LaFave); id., §2.3(f), at 600–603 (“[W]hen the police come on to private property to conduct an investigation or for some other legitimate purpose and restrict their movements to places visitors could be expected to go (e.g., walkways, driveways, porches), observations made from such vantage points are not covered by the Fourth Amendment” (footnotes omitted)).

 

Nor, as a general matter, may a visitor come to the front door in the middle of the night without an express invitation. See State v. Cada, 129 Idaho 224, 233, 923 P. 2d 469, 478 (App. 1996) (“Furtive intrusion late at night or in the predawn hours is not conduct that is expected from ordinary visitors. Indeed, if observed by a resident of the premises, it could be a cause for great alarm”).

 

Similarly, a visitor may not linger at the front door for an extended period. See 9 So. 3d 1, 11 (Fla. App. 2008) (case below) (Cope, J., concurring in part and dissenting in part) (“[T]here is no such thing as squatter’s rights on a front porch. A stranger may not plop down uninvited to spend the afternoon in the front porch rocking chair, or throw down a sleeping bag to spend the night, or lurk on the front porch, looking in the windows”). The license is limited to the amount of time it would customarily take to approach the door, pause long enough to see if someone is home, and (if not expressly invited to stay longer), leave.

 

As I understand the law of trespass and the scope of the implied license, a visitor who adheres to these limitations is not necessarily required to ring the doorbell, knock on the door, or attempt to speak with an occupant. For example, mail carriers, persons making deliveries, and individuals distributing flyers may leave the items they are carrying and depart without making any attempt to converse. A pedestrian or motorist looking for a particular address may walk up to a front door in order to check a house number that is hard to see from the sidewalk or road. A neighbor who knows that the residents are away may approach the door to retrieve an accumulation of newspapers that might signal to a potential burglar that the house is unoccupied.

 

As the majority acknowledges, this implied license to approach the front door extends to the police. See ante, at 6. As we recognized in Kentucky v. King, 563 U. S. ___ (2011), police officers do not engage in a search when they approach the front door of a residence and seek to engage in what is termed a “knock and talk,” i.e., knocking on the door and seeking to speak to an occupant for the purpose of gathering evidence. See id., at ___ (slip op., at 16) (“When law enforcement officers who are not armed with a warrant knock on a door, they do no more than any private citizen might do”). See also 1 LaFave §2.3(e), at 592 (“It is not objectionable for an officer to come upon that part of the property which has been opened to public common use” (internal quotation marks omitted)). Even when the objective of a “knock and talk” is to obtain evidence that will lead to the homeowner’s arrest and prosecution, the license to approach still applies. In other words, gathering evidence—even damning evidence—is a lawful activity that falls within the scope of the license to approach. And when officers walk up to the front door of a house, they are permitted to see, hear, and smell whatever can be detected from a lawful vantage point. California v. Ciraolo, 476 U. S. 207, 213 (1986) (“The Fourth Amendment protection of the home has never been extended to require law enforcement officers to shield their eyes when passing by a home on public thoroughfares”); Cada, supra,at 232, 923 P. 2d, at 477 (“[P]olice officers restricting their activity to [areas to which the public is impliedly invited]are permitted the same intrusion and the same level of observation as would be expected from a reasonably respectful citizen” (internal quotation marks omitted)); 1LaFave §§2.2(a), 2.3(c), at 450–452, 572–577.

B

 

Detective Bartelt did not exceed the scope of the license to approach respondent’s front door. He adhered to the customary path; he did not approach in the middle of the night; and he remained at the front door for only a very short period (less than a minute or two).The Court concludes that Detective Bartelt went too far because he had the “objectiv[e] . . . purpose to conduct a search.” Ante, at 8 (emphasis added). What this means, I take it, is that anyone aware of what Detective Bartelt did would infer that his subjective purpose was to gather evidence. But if this is the Court’s point, then a standard“ knock and talk” and most other police visits would likewise constitute searches. With the exception of visits to serve warrants or civil process, police almost always approach homes with a purpose of discovering information. That is certainly the objective of a “knock and talk.” The Court offers no meaningful way of distinguishing the “objective purpose” of a “knock and talk” from the “objective purpose” of Detective Bartelt’s conduct here.

 

The Court contends that a “knock and talk” is different because it involves talking, and “all are invited” to do that. Ante, at 7–8, n. 4 (emphasis deleted). But a police officer who approaches the front door of a house in accordance with the limitations already discussed may gather evidence by means other than talking. The officer may observe items in plain view and smell odors coming from the house. Ciraolo, supra, at 213; Cada, 129 Idaho, at 232, 923 P. 2d, at 477; 1 LaFave §§2.2(a), 2.3(c), at 450–452, 572–577. So the Court’s “objective purpose” argument cannot stand.

 

What the Court must fall back on, then, is the particular instrument that Detective Bartelt used to detect the odor of marijuana, namely, his dog. But in the entire body of common-law decisions, the Court has not found a single case holding that a visitor to the front door of a home commits a trespass if the visitor is accompanied by a dog on a leash. On the contrary, the common law allowed even unleashed dogs to wander on private property without committing a trespass. G. Williams, Liability for Animals 136–146 (1939); J. Ingham, A Treatise on Property in Animals Wild and Domestic and the Rights and Responsibilities Arising Therefrom 277–278 (1900). Cf. B. Markesinis & S. Deakin, Tort Law 511 (4th ed. 1999).

 

The Court responds that “[i]t is not the dog that is the problem, but the behavior that here involved use of the dog.” Ante, at 7, n. 3. But where is the support in the law of trespass for this proposition? Dogs’ keen sense of smell has been used in law enforcement for centuries. The antiquity of this practice is evidenced by a Scottish law from 1318 that made it a crime to “disturb a tracking dog or the men coming with it for pursuing thieves or seizing malefactors.” K. Brown et al., The Records of the Parliaments of Scotland to 1707, (St Andrews, 2007–2013), online at http://www.rps.ac.uk/mss/1318/9 . If bringing a tracking dog to the front door of a home constituted a trespass, one would expect at least one case to have arisen during the past 800 years. But the Court has found none.

For these reasons, the real law of trespass provides no support for the Court’s holding today. While the Court claims that its reasoning has “ancient and durable roots,” ante, at 4, its trespass rule is really a newly struck counterfeit.

 

III

 

The concurring opinion attempts to provide an alternative ground for today’s decision, namely, that Detective Bartelt’s conduct violated respondent’s reasonable expectations of privacy. But we have already rejected a very similar, if not identical argument, see Illinois v. Caballes, 543 U. S. 405, 409–410 (2005), and in any event I see no basis for concluding that the occupants of a dwelling have a reasonable expectation of privacy in odors that emanate from the dwelling and reach spots where members of the public may lawfully stand. It is clear that the occupant of a house has no reasonable expectation of privacy with respect to odors that can be smelled by human beings who are standing in such places. See United States v. Johns, 469 U. S. 478, 482 (1985) (“After the officers came closer and detected the distinct odor of marihuana, they had probable cause to believe that the vehicles contained contraband”); United States v. Ventresca, 380 U. S. 102, 111 (1965) (scent of fermenting mash supported probable cause for warrant); United States v. Johnston, 497 F. 2d 397, 398 (CA9 1974) (there is no “reasonable expectation of privacy from drug agents with inquisitive nostrils”). And I would not draw a line between odors that can be smelled by humans and those that are detectible only by dogs.

 

Consider the situation from the point of view of the occupant of a building in which marijuana is grown or methamphetamine is manufactured. Would such an occupant reason as follows? “I know that odors may emanate from my building and that atmospheric conditions, such as the force and direction of the wind, may affect the strength of those odors when they reach a spot where members of the public may lawfully stand. I also know that some people have a much more acute sense of smell than others,6 and I have no idea who might be standing in one of the spots in question when the odors from my house reach that location. In addition, I know that odors coming from my building, when they reach these locations, may be strong enough to be detected by a dog. But I am confident that they will be so faint that they cannot be smelled by any human being.” Such a finely tuned expectation would be entirely unrealistic, and I see no evidence that society is prepared to recognize it as reasonable.

 

In an attempt to show that respondent had a reasonable expectation of privacy in the odor of marijuana wafting from his house, the concurrence argues that this case is just like Kyllo v. United States, 533 U. S. 27 (2001), which held that police officers conducted a search when they used a thermal imaging device to detect heat emanating from a house. Ante, at 3–4 (opinion of KAGAN, J.). This Court, however, has already rejected the argument that the use of a drug-sniffing dog is the same as the use of a thermal imaging device. See Caballes, 543 U. S., at 409–410. The very argument now advanced by the concurrence appears in Justice Souter’s Caballes dissent. See id., at 413, and n. 3. But the Court was not persuaded.

6. Some humans naturally have a much more acute sense of smell than others, and humans can be trained to detect and distinguish odors that could not be detected without such training. See E. Hancock, A Primer on Smell, http://www.jhu.edu/jhumag/996web/smell.html . Some individuals employed in the perfume and wine industries, for example, have an amazingly acute sense of smell. Ibid.

 

 

Contrary to the interpretation propounded by the concurrence, Kyllo is best understood as a decision about the use of new technology. The Kyllo Court focused on the fact that the thermal imaging device was a form of “sense enhancing technology” that was “not in general publicuse,” and it expressed concern that citizens would be “at the mercy of advancing technology” if its use was not restricted. 533 U. S., at 34–35. A dog, however, is not a new form of “technology or a “device.” And, as noted, the use of dogs’ acute sense of smell in law enforcement dates back many centuries.

 

The concurrence suggests that a Kyllo-based decision would be “much like” the actual decision of the Court, but that is simply not so. The holding of the Court is based on what the Court sees as a “‘physical intrusion of a constitutionally protected area.’” Ante, at 3 (quoting United States v. Knotts, 460 U. S. 276, 286 (1983) (Brennan, J., concurring in judgment)). As a result, it does not apply when a dog alerts while on a public sidewalk or street or in the corridor of a building to which the dog and handler have been lawfully admitted.

 

The concurrence’s Kyllo-based approach would have a much wider reach. When the police used the thermal imaging device in Kyllo, they were on a public street, 533 U. S., at 29, and “committed no trespass.” Ante, at 3. Therefore, if a dog’s nose is just like a thermal imaging device for Fourth Amendment purposes, a search would occur if a dog alerted while on a public sidewalk or in the corridor of an apartment building. And the same would be true if the dog was trained to sniff, not for marijuana, but for more dangerous quarry, such as explosives or for a violent fugitive or kidnaped child. I see no ground for hampering legitimate law enforcement in this way.

 

IV

 

The conduct of the police officer in this case did not constitute a trespass and did not violate respondent’s reasonable expectations of privacy. I would hold that this conduct was not a search, and I therefore respectfully dissent.