Justice Powell, with whom Justice Brennan, Justice Marshall, and Justice Blackmun join, dissenting.
Concurring in Katz v. United States, 389 U.S. 347 (1967), Justice Harlan warned that any decision to construe the Fourth Amendment as proscribing only physical intrusions by police onto private property "is, in the present day, bad physics as well as bad law, for reasonable expectations of privacy may be defeated by electronic as well as physical invasion." Id., at 362. Because the Court today ignores that warning in an opinion that departs significantly from the standard developed in Katz for deciding when a Fourth Amendment violation has occurred, I dissent.
As the Court's opinion reflects, the facts of this case are not complicated. Officer Shutz investigated an anonymous report that marijuana was growing in the backyard of respondent's home. A tall fence prevented Shutz from looking into the yard from the street. The yard was directly behind the home so that the home itself furnished one border of the fence. Shutz proceeded, without obtaining a warrant, to charter a plane and fly over the home at an altitude of 1,000 feet. Observing marijuana plants growing in the fenced-in yard, Shutz photographed respondent's home and yard, as well as homes and yards of neighbors. The photograph clearly shows that the enclosed yard also contained a small swimming pool and patio. Shutz then filed an affidavit, to which he attached the photograph, describing the anonymous tip and his aerial observation of the marijuana. A warrant issued, and a search of the yard confirmed Shutz' aerial observations. Respondent was arrested for cultivating marijuana, a felony under California law.
Respondent contends that the police intruded on his constitutionally protected expectation of privacy when they conducted aerial surveillance of his home and photographed his backyard without first obtaining a warrant. The Court rejects that contention, holding that respondent's expectation of privacy in the curtilage of his home, although reasonable as to intrusions on the ground, was unreasonable as to surveillance from the navigable airspace. In my view, the Court's holding rests on only one obvious fact, namely, that the airspace generally is open to all persons for travel in airplanes. The Court does not explain why this single fact deprives citizens of their privacy interest in outdoor activities in an enclosed curtilage.
The Fourth Amendment protects "[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures." While the familiar history of the Amendment need not be recounted here, we should remember that it reflects a choice that our society should be one in which citizens "dwell in reasonable security and freedom from surveillance." Johnson v. United States, 333 U.S. 10, 14 (1948). Since that choice was made by the Framers of the Constitution, our cases construing the Fourth Amendment have relied in part on the common law for instruction on "what sorts of searches the Framers...regarded as reasonable." Steagald v. United States, 451 U.S. 204, 217 (1981). But we have repeatedly refused to freeze "'into constitutional law those enforcement practices that existed at the time of the Fourth Amendment's passage.'" Id., at 217, n. 10, quoting Payton v. New York, 445 U.S. 573, 591, n. 33 (1980). See United States v. United States District Court, 407 U.S. 297, 313 (1972). Rather, we have construed the Amendment "'in light of contemporary norms and conditions,'" Steagald v. United States, supra, at 217, n. 10, quoting Payton v. New York, supra, at 591, n. 33, in order to prevent "any stealthy encroachments" on our citizens' right to be free of arbitrary official intrusion, Boyd v. United States, 116 U.S. 616, 635 (1886). Since the landmark decision in Katz v. United States, the Court has fulfilled its duty to protect Fourth Amendment rights by asking if police surveillance has intruded on an individual's reasonable expectation of privacy.
As the decision in Katz held, and dissenting opinions written by Justices of this Court prior to Katz recognized, e. g., Goldman v. United States, 316 U.S. 129, 139-141 (1942) (Murphy, J., dissenting); Olmstead v. United States, 277 U.S. 438, 474 (1928) (Brandeis, J., dissenting), a standard that defines a Fourth Amendment "search" by reference to whether police have physically invaded a "constitutionally protected area" provides no real protection against surveillance techniques made possible through technology. Technological advances have enabled police to see people's activities and associations, and to hear their conversations, without being in physical proximity. Moreover, the capability now exists for police to conduct intrusive surveillance without any physical penetration of the walls of homes or other structures that citizens may believe shelters their privacy. Looking to the Fourth Amendment for protection against such "broad and unsuspected governmental incursions" into the "cherished privacy of law-abiding citizens," United States v. United States District Court, supra, at 312-313 (footnote omitted), the Court in Katz abandoned its inquiry into whether police had committed a physical trespass. Katz announced a standard under which the occurrence of a search turned not on the physical position of the police conducting the surveillance, but on whether the surveillance in question had invaded a constitutionally protected reasonable expectation of privacy.
Our decisions following the teaching of Katz illustrate that this inquiry "normally embraces two discrete questions." Smith v. Maryland, 442 U.S. 735, 740 (1979). "The first is whether the individual, by his conduct, has 'exhibited an actual (subjective) expectation of privacy.'" Ibid., quoting Katz v. United States, 389 U.S., at 361 (Harlan, J., concurring). The second is whether that subjective expectation "is 'one that society is prepared to recognize as "reasonable."'" 442 U.S., at 740, quoting Katz v. United States, supra, at 361 (Harlan, J., concurring). While the Court today purports to reaffirm this analytical framework, its conclusory rejection of respondent's expectation of privacy in the yard of his residence as one that "is unreasonable," ante, at 213, represents a turning away from the principles that have guided our Fourth Amendment inquiry. The Court's rejection of respondent's Fourth Amendment claim is curiously at odds with its purported reaffirmation of the curtilage doctrine, both in this decision and its companion case, Dow Chemical Co. v. United States, post, p. 227, and particularly with its conclusion in Dow that society is prepared to recognize as reasonable expectations of privacy in the curtilage, post, at 235.
The second question under Katz has been described as asking whether an expectation of privacy is "legitimate in the sense required by the Fourth Amendment." Oliver v. United States, 466 U.S. 170, 182 (1984). The answer turns on "whether the government's intrusion infringes upon the personal and societal values protected by the Fourth Amendment." Id., at 182-183. While no single consideration has been regarded as dispositive, "the Court has given weight to such factors as the intention of the Framers of the Fourth Amendment,...the uses to which the individual has put a location,...and our societal understanding that certain areas deserve the most scrupulous protection from government invasion." Id., at 178. Our decisions have made clear that this inquiry often must be decided by "reference to a 'place,'" Katz v. United States, supra, at 361 (Harlan, J., concurring); see Payton v. New York, 445 U.S., at 589, and that a home is a place in which a subjective expectation of privacy virtually always will be legitimate, ibid.; see, e. g., United States v. Karo, 468 U.S. 705, 713-715 (1984); Steagald v. United States, 451 U.S., at 211-212. "At the very core [of the Fourth Amendment] stands the right of a [person] to retreat into his own home and there be free from unreasonable governmental intrusion." Silverman v. United States, 365 U.S. 505, 511 (1961).
This case involves surveillance of a home, for as we stated in Oliver v. United States, the curtilage "has been considered part of the home itself for Fourth Amendment purposes." 466 U.S., at 180. In Dow Chemical Co. v. United States, decided today, the Court reaffirms that the "curtilage doctrine evolved to protect much the same kind of privacy as that covering the interior of a structure." Post, at 235. The Court in Dow emphasizes, moreover, that society accepts as reasonable citizens' expectations of privacy in the area immediately surrounding their homes. Ibid.
In deciding whether an area is within the curtilage, courts "have defined the curtilage, as did the common law, by reference to the factors that determine whether an individual reasonably may expect that an area immediately adjacent to the home will remain private. See, e. g., United States v. Van Dyke, 643 F.2d 992, 993-994 (CA4 1981); United States v. Williams, 581 F.2d 451, 453 (CA5 1978); Care v. United States, 231 F.2d 22, 25 (CA10), cert. denied, 351 U.S. 932 (1956)." Oliver v. United States, supra, at 180. The lower federal courts have agreed that the curtilage is "an area of domestic use immediately surrounding a dwelling and usually but not always fenced in with the dwelling." United States v. LaBerge, 267 F. Supp. 686, 692 (Md. 1967); see United States v. Van Dyke, 643 F.2d 992, 993, n. 1 (CA4 1984). Those courts also have held that whether an area is within the curtilage must be decided by looking at all of the facts. Ibid., citing Care v. United States, supra, at 25. Relevant facts include the proximity between the area claimed to be curtilage and the home, the nature of the uses to which the area is put, and the steps taken by the resident to protect the area from observation by people passing by. See Care v. United States, supra, at 25; see also United States v. Van Dyke, supra, at 993-994.
The Court begins its analysis of the Fourth Amendment issue posed here by deciding that respondent had an expectation of privacy in his backyard. I agree with that conclusion because of the close proximity of the yard to the house, the nature of some of the activities respondent conducted there, and because he had taken steps to shield those activities from the view of passersby. The Court then implicitly acknowledges that society is prepared to recognize his expectation as reasonable with respect to ground-level surveillance, holding that the yard was within the curtilage, an area in which privacy interests have been afforded the "most heightened" protection. Ante, at 213. As the foregoing discussion of the curtilage doctrine demonstrates, respondent's yard unquestionably was within the curtilage. Since Officer Shutz could not see into this private family area from the street, the Court certainly would agree that he would have conducted an unreasonable search had he climbed over the fence, or used a ladder to peer into the yard without first securing a warrant. See United States v. Van Dyke, supra; see also United States v. Williams, 581 F.2d 451 (CA5 1978).
The Court concludes, nevertheless, that Shutz could use an airplane--a product of modern technology--to intrude visually into respondent's yard. The Court argues that respondent had no reasonable expectation of privacy from aerial observation. It notes that Shutz was "within public navigable airspace," ante, at 213, when he looked into and photographed respondent's yard. It then relies on the fact that the surveillance was not accompanied by a physical invasion of the curtilage, ibid. Reliance on the manner of surveillance is directly contrary to the standard of Katz, which identifies a constitutionally protected privacy right by focusing on the interests of the individual and of a free society. Since Katz, we have consistently held that the presence or absence of physical trespass by police is constitutionally irrelevant to the question whether society is prepared to recognize an asserted privacy interest as reasonable. E. g., United States v. United States District Court, 407 U.S., at 313.
The Court's holding, therefore, must rest solely on the fact that members of the public fly in planes and may look down at homes as they fly over them. Ante, at 213-214. The Court does not explain why it finds this fact to be significant. One may assume that the Court believes that citizens bear the risk that air travelers will observe activities occurring within backyards that are open to the sun and air. This risk, the Court appears to hold, nullifies expectations of privacy in those yards even as to purposeful police surveillance from the air. The Court finds support for this conclusion in United States v. Knotts, 460 U.S. 276 (1983). Ante, at 213.
This line of reasoning is flawed. First, the actual risk to privacy from commercial or pleasure aircraft is virtually nonexistent. Travelers on commercial flights, as well as private planes used for business or personal reasons, normally obtain at most a fleeting, anonymous, and nondiscriminating glimpse of the landscape and buildings over which they pass. The risk that a passenger on such a plane might observe private activities, and might connect those activities with particular people, is simply too trivial to protect against. It is no accident that, as a matter of common experience, many people build fences around their residential areas, but few build roofs over their backyards. Therefore, contrary to the Court's suggestion, ante, at 213, people do not "'knowingly expos[e]'" their residential yards "'to the public'" merely by failing to build barriers that prevent aerial surveillance.
The Court's reliance on Knotts reveals the second problem with its analysis. The activities under surveillance in Knotts took place on public streets, not in private homes. 460 U.S., at 281-282. Comings and goings on public streets are public matters, and the Constitution does not disable police from observing what every member of the public can see. The activity in this case, by contrast, took place within the private area immediately adjacent to a home. Yet the Court approves purposeful police surveillance of that activity and area similar to that approved in Knotts with respect to public activities and areas. The only possible basis for this holding is a judgment that the risk to privacy posed by the remote possibility that a private airplane passenger will notice outdoor activities is equivalent to the risk of official aerial surveillance. But the Court fails to acknowledge the qualitative difference between police surveillance and other uses made of the airspace. Members of the public use the airspace for travel, business, or pleasure, not for the purpose of observing activities taking place within residential yards. Here, police conducted an overflight at low altitude solely for the purpose of discovering evidence of crime within a private enclave into which they were constitutionally forbidden to intrude at ground level without a warrant. It is not easy to believe that our society is prepared to force individuals to bear the risk of this type of warrantless police intrusion into their residential areas.
Since respondent had a reasonable expectation of privacy in his yard, aerial surveillance undertaken by the police for the purpose of discovering evidence of crime constituted a "search" within the meaning of the Fourth Amendment. "Warrantless searches are presumptively unreasonable, though the Court has recognized a few limited exceptions to this general rule." United States v. Karo, 468 U.S., at 717. This case presents no such exception. The indiscriminate nature of aerial surveillance, illustrated by Officer Shutz' photograph of respondent's home and enclosed yard as well as those of his neighbors, poses "far too serious a threat to privacy interests in the home to escape entirely some sort of Fourth Amendment oversight." Id., at 716 (footnote omitted). Therefore, I would affirm the judgment of the California Court of Appeal ordering suppression of the marijuana plants.
Some may believe that this case, involving no physical intrusion on private property, presents "the obnoxious thing in its mildest and least repulsive form." Boyd v. United States, 116 U.S., at 635. But this Court recognized long ago that the essence of a Fourth Amendment violation is "not the breaking of [a person's] doors, and the rummaging of his drawers," but rather is "the invasion of his indefeasible right of personal security, personal liberty and private property." Id., at 630. Rapidly advancing technology now permits police to conduct surveillance in the home itself, an area where privacy interests are most cherished in our society, without any physical trespass. While the rule in Katz was designed to prevent silent and unseen invasions of Fourth Amendment privacy rights in a variety of settings, we have consistently afforded heightened protection to a person's right to be left alone in the privacy of his house. The Court fails to enforce that right or to give any weight to the longstanding presumption that warrantless intrusions into the home are unreasonable. I dissent.
- . The warrant authorized Shutz to search the home and its attached garage, as well as the yard, for marijuana, narcotics paraphernalia, records relating to marijuana sales, and documents identifying the occupant of the premises.
- . See, e. g., Payton v. New York, 445 U.S. 573, 583-585, n. 20 (1980).
- . As was said more than four decades ago: "[T]he search of one's home or office no longer requires physical entry for science has brought forth far more effective devices for the invasion of a person's privacy than the direct and obvious methods of oppression which were detested by our forbears and which inspired the Fourth Amendment.... Whether the search of private quarters is accomplished by placing on the outer walls of the sanctum a detectaphone that transmits to the outside listener the intimate details of a private conversation, or by new methods of photography that penetrate walls or overcome distances, the privacy of the citizen is equally invaded by the Government and intimate personal matters are laid bare to view." Goldman v. United States, 316 U.S. 129, 139 (1942) (Murphy, J., dissenting). Since 1942, science has developed even more sophisticated means of surveillance.
- . In Justice Harlan's classic description, an actual expectation of privacy is entitled to Fourth Amendment protection if it is an expectation that society recognizes as "reasonable." Katz v. United States, 389 U.S., at 361 (Harlan, J., concurring). Since Katz, our decisions also have described constitutionally protected privacy interests as those that society regards as "legitimate," using the words "reasonable" and "legitimate" interchangeably. E. g., Oliver v. United States, 466 U.S. 170 (1984); Rakas v. Illinois, 439 U.S. 128, 143-144, n. 12 (1978).
- . "Legitimation of expectations of privacy by law must have a source outside of the Fourth Amendment, either by reference to concepts of real or personal property law or to understandings that are recognized and permitted by society." Ibid. This inquiry necessarily focuses on personal interests in privacy and liberty recognized by a free society.
- . The Oxford English Dictionary defines curtilage as "a small court, yard, garth, or piece of ground attached to a dwelling-house, and forming one enclosure with it, or so regarded by the law; the area attached to and containing a dwelling-house and its out-buildings." 2 Oxford English Dictionary 1278 (1933).
- . The Court omits any reference to the fact that respondent's yard contained a swimming pool and a patio for sunbathing and other private activities. At the suppression hearing, respondent sought to introduce evidence showing that he did use his yard for domestic activities. The trial court refused to consider that evidence. Tr. on Appeal 5-8 (Aug. 15, 1983).
- . Of course, during takeoff and landing, planes briefly fly at low enough altitudes to afford fleeting opportunities to observe some types of activity in the curtilages of residents who live within the strictly regulated takeoff and landing zones. As all of us know from personal experience, at least in passenger aircrafts, there rarely--if ever--is an opportunity for a practical observation and photographing of unlawful activity similar to that obtained by Officer Shutz in this case. The Court's analogy to commercial and private overflights, therefore, is wholly without merit.
- . Some of our precedents have held that an expectation of privacy was not reasonable in part because the individual had assumed the risk that certain kinds of private information would be turned over to the police. United States v. Miller, 425 U.S. 435, 443 (1976). None of the prior decisions of this Court is a precedent for today's decision. As Justice Marshall has observed, it is our duty to be sensitive to the risks that a citizen "should be forced to assume in a free and open society." Smith v. Maryland, 442 U.S. 735, 750 (1979) (dissenting opinion).
- . The Court's decision has serious implications for outdoor family activities conducted in the curtilage of a home. The feature of such activities that makes them desirable to citizens living in a free society, namely, the fact that they occur in the open air and sunlight, is relied on by the Court as a justification for permitting police to conduct warrantless surveillance at will. Aerial surveillance is nearly as intrusive on family privacy as physical trespass into the curtilage. It would appear that, after today, families can expect to be free of official surveillance only when they retreat behind the walls of their homes.
- . Of course, the right of privacy in the home and its curtilage includes no right to engage in unlawful conduct there. But the Fourth Amendment requires police to secure a warrant before they may intrude on that privacy to search for evidence of suspected crime. United States v. Karo, 468 U.S. 705, 713-715 (1984).