Opinion

JUSTICE O'CONNOR, concurring in the judgment.

I concur in the judgment reversing the Supreme Court of Florida because I agree that police observation of the greenhouse in Riley's curtilage from a helicopter passing at an altitude of 400 feet did not violate an expectation of privacy "that society is prepared to recognize as reasonable.'" Katz v. United States, 389 U. S. 347, 389 U. S. 361 (1967) (Harlan, J., concurring). I write separately, however, to clarify the standard I believe follows from California v. Ciraolo, 476 U. S. 207 (1986). In my view, the plurality's approach rests the scope of Fourth Amendment protection too heavily on compliance with FAA regulations whose purpose is to promote air safety, not to protect "[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures." U.S.Const., Amdt. 4.

Ciraolo involved observation of curtilage by officers flying in an airplane at an altitude of 1,000 feet. In evaluating whether this observation constituted a search for which a warrant was required, we acknowledged the importance of curtilage in Fourth Amendment doctrine:

The protection afforded the curtilage is essentially a protection of families and personal privacy in an area intimately linked to the home, both physically and psychologically, where privacy expectations are most heightened.

476 U.S. at 476 U. S. 212 -213. Although the curtilage is an area to which the private activities of the home extend, all police observation of the curtilage is not necessarily barred by the Fourth Amendment. As we observed:

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.

Id. at 476 U. S. 213. In Ciraolo, we likened observation from a plane traveling in "public navigable airspace" at 1,000 feet to observation by police "passing by a home on public thoroughfares." We held that "[i]n an age where private and commercial flight in the public airways is routine," it is unreasonable to expect the curtilage to be constitutionally protected from aerial observation with the naked eye from an altitude of 1,000 feet. Id. at 476 U. S. 215.

Ciraolo's expectation of privacy was unreasonable not because the airplane was operating where it had a "right to be," but because public air travel at 1,000 feet is a sufficiently routine part of modern life that it is unreasonable for persons on the ground to expect that their curtilage will not be observed from the air at that altitude. Although "helicopters are not bound by the lower limits of the navigable airspace allowed to other aircraft," ante at 488 U. S. 451, there is no reason to assume that compliance with FAA regulations alone determines " whether the government's intrusion infringes upon the personal and societal values protected by the Fourth Amendment.'" Ciraolo, supra, at 476 U. S. 212 (quoting Oliver v. United States, 466 U. S. 170, 466 U. S. 182 -183 (1984)). Because the FAA has decided that helicopters can lawfully operate at virtually any altitude so long as they pose no safety hazard, it does not follow that the expectations of privacy "society is prepared to recognize as `reasonable'" simply mirror the FAA's safety concerns.

Observations of curtilage from helicopters at very low altitudes are not perfectly analogous to ground-level observations from public roads or sidewalks. While in both cases the police may have a legal right to occupy the physical space from which their observations are made, the two situations are not necessarily comparable in terms of whether expectations of privacy from such vantage points should be considered reasonable. Public roads, even those less traveled by, are clearly demarked public thoroughfares. Individuals who seek privacy can take precautions, tailored to the location of the road, to avoid disclosing private activities to those who pass by. They can build a tall fence, for example, and thus ensure private enjoyment of the curtilage without risking public observation from the road or sidewalk. If they do not take such precautions, they cannot reasonably expect privacy from public observation. In contrast, even individuals who have taken effective precautions to ensure against ground-level observations cannot block off all conceivable aerial views of their outdoor patios and yards without entirely giving up their enjoyment of those areas. To require individuals to completely cover and enclose their curtilage is to demand more than the "precautions customarily taken by those seeking privacy." Rakas v. Illinois, 439 U. S. 128, 439 U. S. 152 (1978) (Powell, J., concurring). The fact that a helicopter could conceivably observe the curtilage at virtually any altitude or angle, without violating FAA regulations, does not in itself mean that an individual has no reasonable expectation of privacy from such observation.

In determining whether Riley had a reasonable expectation of privacy from aerial observation, the relevant inquiry after Ciraolo is not whether the helicopter was where it had a right to be under FAA regulations. Rather, consistent with Katz, we must ask whether the helicopter was in the public airways at an altitude at which members of the public travel with sufficient regularity that Riley's expectation of privacy from aerial observation was not "one that society is prepared to recognize as reasonable.'" Katz, supra, at 361. Thus, in determining "`whether the government's intrusion infringes upon the personal and societal values protected by the Fourth Amendment,'" Ciraolo, supra, at 476 U. S. 212 (quoting Oliver, supra, at 466 U. S. 182 -183), it is not conclusive to observe, as the plurality does, that "[a]ny member of the public could legally have been flying over Riley's property in a helicopter at the altitude of 400 feet, and could have observed Riley's greenhouse." Ante at 451. Nor is it conclusive that police helicopters may often fly at 400 feet. If the public rarely, if ever, travels overhead at such altitudes, the observation cannot be said to be from a vantage point generally used by the public, and Riley cannot be said to have "knowingly expose[d]" his greenhouse to public view. However, if the public can generally be expected to travel over residential backyards at an altitude of 400 feet, Riley cannot reasonably expect his curtilage to be free from such aerial observation.

In my view, the defendant must bear the burden of proving that his expectation of privacy was a reasonable one, and thus that a "search" within the meaning of the Fourth Amendment even took place. Cf. Jones v. United States, 362 U. S. 257, 362 U. S. 261 (1960) ("Ordinarily, then, it is entirely proper to require of one who seeks to challenge the legality of a search as the basis for suppressing relevant evidence that he allege, and if the allegation be disputed that he establish, that he himself was the victim of an invasion of privacy"); Nardone v. United States, 308 U. S. 338, 308 U. S. 341 (1939).

Because there is reason to believe that there is considerable public use of airspace at altitudes of 400 feet and above, and because Riley introduced no evidence to the contrary before the Florida courts, I conclude that Riley's expectation that his curtilage was protected from naked-eye aerial observation from that altitude was not a reasonable one. However, public use of altitudes lower than that -particularly public observations from helicopters circling over the curtilage of a home -may be sufficiently rare that police surveillance from such altitudes would violate reasonable expectations of privacy, despite compliance with FAA air safety regulations