with whom Justice Marshall joins, dissenting.
This case presents two questions: first whether law enforcement officers may conduct a warrantless search of the *134contents of a container merely because a private party has previously examined the container’s contents and informed the officers of its suspicious nature; and second, whether law enforcement officers may conduct a chemical field test of a substance once the officers have legitimately located the substance. Because I disagree with the Court's treatment of each of these issues, I respectfully dissent.
I
I agree entirely with Justice White that the Court has expanded the reach of the private-search doctrine far beyond its logical bounds. Ante, at 127-133 (White, J., concurring in judgment). It is difficult to understand how respondents can be said to have no expectation of privacy in a closed container simply because a private party has previously opened the container and viewed its contents. I also agree with Justice White, however, that if the private party presents the contents of a container to a law enforcement officer in such a manner that the contents are plainly visible, the officer’s visual inspection of the contents does not constitute a “search” within the meaning of the Fourth Amendment. Because the record in this case is unclear on the question whether the contents of respondents’ package were plainly visible when the Federal Express employee showed the package to the DEA officer, I would remand the case for further factfinding on this central issue.
II
As noted, I am not persuaded that the DEA officer actually came upon respondents’ cocaine without violating the Fourth Amendment and, accordingly, I need not address the legality of the chemical field test. Since the Court has done so, however, I too will address the question, assuming, arguendo, that the officer committed neither an unconstitutional search nor an unconstitutional seizure prior to the point at which he took the sample of cocaine out of the plastic bags to conduct the test.
*135A
I agree that, under the hypothesized circumstances, the field test in this case was not a search within the meaning of the Fourth Amendment for the following reasons: First, the officer came upon the white powder innocently; second, under the hypothesized circumstances, respondents could not have had a reasonable expectation of privacy in the chemical identity of the powder because the DEA agents were already able to identify it as contraband with virtual certainty, Texas v. Brown, 460 U. S. 730, 750-751 (1983) (Stevens, J., concurring in judgment); and third, the test required the destruction of only a minute quantity of the powder. The Court, however, has reached this conclusion on a much broader ground, relying on two factors alone to support the proposition that the field test was not a search: First, the fact that the test revealed only whether or not the substance was cocaine, without providing any further information; and second, the assumption that an individual does not have a reasonable expectation of privacy in such a fact.
The Court asserts that its “conclusion is dictated by United States v. Place,” ante, at 123, in which the Court stated that a “canine sniff” of a piece of luggage did not constitute a search because it “is much less intrusive than a typical search,” and because it “discloses only the presence or absence of narcotics, a contraband item.” 462 U. S. 696, 707 (1983). Presumably, the premise of Place was that an individual could not have a reasonable expectation of privacy in the presence or absence of narcotics in his luggage. The validity of the canine sniff in that case, however, was neither briefed by the parties nor addressed by the courts below. Indeed, since the Court ultimately held that the defendant’s luggage had been impermissibly seized, its discussion of the question was wholly unnecessary to its judgment. In short, as Justice Blackmun pointed out at the time, “[t]he Court [was] certainly in no position to consider all the ramifications of this important issue.” Id., at 723-724.
*136Nonetheless, the Court concluded:
“[T]he 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. Therefore, we conclude that the particular course of investigation that the agents intended to pursue here — exposure of respondent’s luggage, which was located in a public place, to a trained canine — did not constitute a ‘search’ within the meaning of the Fourth Amendment.” Id., at 707.
As it turns out, neither the Court’s knowledge nor its imagination regarding criminal investigative techniques proved very sophisticated, for within one year we have learned of another investigative procedure that shares with the dog sniff the same defining characteristics that led the Court to suggest that the dog sniff was not a search.
Before continuing along the course that the Court so hastily charted in Place, it is only prudent to take this opportunity — in my view, the first real opportunity — to consider the implications of the Court’s new Fourth Amendment jurisprudence. Indeed, in light of what these two cases have taught us about contemporary law enforcement methods, it is particularly important that we analyze the basis upon which the Court has redefined the term “search” to exclude a broad class of surveillance techniques. In my view, such an analysis demonstrates that, although the Court’s conclusion is correct in this case, its dictum in Place was dangerously incorrect. More important, however, the Court’s reasoning in both cases is fundamentally misguided and could potentially lead to the development of a doctrine wholly at odds with the principles embodied in the Fourth Amendment.
Because the requirements of the Fourth Amendment apply only to “searches” and “seizures,” an investigative technique *137that falls within neither category need not be reasonable and may be employed without a warrant and without probable cause, regardless of the circumstances surrounding its use. The prohibitions of the Fourth Amendment are not, however, limited to any preconceived conceptions of what constitutes a search or a seizure; instead we must apply the constitutional language to modern developments according to the fundamental principles that the Fourth Amendment embodies. Katz v. United States, 389 U. S. 347 (1967). See Amsterdam, Perspectives on the Fourth Amendment, 58 Minn. L. Rev. 349, 356 (1974). Before excluding a class of surveillance techniques from the reach of the Fourth Amendment, therefore, we must be certain that none of the techniques so excluded threatens the areas of personal security and privacy that the Amendment is intended to protect.
What is most startling about the Court’s interpretation of the term “search,” both in this case and in Place, is its exclusive focus on the nature of the information or item sought and revealed through the use of a surveillance technique, rather than on the context in which the information or item is concealed. Combining this approach with the blanket assumption, implicit in Place and explicit in this case, that individuals in our society have no reasonable expectation of privacy in the fact that they have contraband in their possession, the Court adopts a general rule that a surveillance technique does not constitute a search if it reveals only whether or not an individual possesses contraband.
It is certainly true that a surveillance technique that identifies only the presence or absence of contraband is less intrusive than a technique that reveals the precise nature of an item regardless of whether it is contraband. But by seizing upon this distinction alone to conclude that the first type of technique, as a general matter, is not a search, the Court has foreclosed any consideration of the circumstances under which the technique is used, and may very well have paved *138the way for technology to override the limits of law in the area of criminal investigation.
For example, under the Court’s analysis in these cases, law enforcement officers could release a trained cocaine-sensitive dog — to paraphrase the California Court of Appeal, a “canine cocaine connoisseur” — to roam the streets at random, alerting the officers to people carrying cocaine. Cf. People v. Evans, 65 Cal. App. 3d 924, 932, 134 Cal. Rptr. 436, 440 (1977). Or, if a device were developed that, when aimed at a person, would detect instantaneously whether the person is carrying cocaine, there would be no Fourth Amendment bar, under the Court’s approach, to the police setting up such a device on a street corner and scanning all passersby. In fact, the Court’s analysis is so unbounded that if a device were developed that could detect, from the outside of a building, the presence of cocaine inside, there would be no constitutional obstacle to the police cruising through a residential neighborhood and using the device to identify all homes in which the drug is present. In short, under the interpretation of the Fourth Amendment first suggested in Place and first applied in this case, these surveillance techniques would not constitute searches and therefore could be freely pursued whenever and wherever law enforcement officers desire. Hence, at some point in the future, if the Court stands by the theory it has adopted today, search warrants, probable cause, and even “reasonable suspicion” may very well become notions of the past. Fortunately, we know from precedents such as Katz v. United States, supra, overruling the “trespass” doctrine of Goldman v. United States, 316 U. S. 129 (1942), and Olmstead v. United States, 277 U. S. 438 (1928), that this Court ultimately stands ready to prevent this Orwellian world from coming to pass.
Although the Court accepts, as it must, the fundamental proposition that an investigative technique is a search within the meaning of the Fourth Amendment if it intrudes upon a privacy expectation that society considers to be reasonable, *139ante, at 113, the Court has entirely omitted from its discussion the considerations that have always guided our decisions in this area. In determining whether a reasonable expectation of privacy has been violated, we have always looked to the context in which an item is concealed, not to the identity of the concealed item. Thus in cases involving searches for physical items, the Court has framed its analysis first in terms of the expectation of privacy that normally attends the location of the item and ultimately in terms of the legitimacy of that expectation. In United States v. Chadwick, 433 U. S. 1 (1977), for example, we held that “[n]o less than one who locks the doors of his home against intruders, one who safeguards his possessions [by locking them in a footlocker] is due the protection of the Fourth Amendment. . . .” Id., at 11. Our holding was based largely on the observation that, “[b]y placing personal effects inside a double-locked footlocker, respondents manifested an expectation that the contents would remain free from public examination.” Ibid. The Court made the same point in United States v. Ross, 456 U. S. 798, 822-823 (1982), where it held that the “Fourth Amendment provides protection to the owner of every container that conceals its contents from plain view.” The fact that a container contains contraband, which indeed it usually does in such cases, has never altered our analysis.
Similarly, in Katz v. United States, we held that electronic eavesdropping constituted a search under the Fourth Amendment because it violated a reasonable expectation of privacy. In reaching that conclusion, we focused upon the private context in which the conversation in question took place, stating: “What a person knowingly exposes to the public ... is not a subject of Fourth Amendment protection. . . . But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.” 389 U. S., at 351-352. Again, the fact that the conversations involved in Katz were incriminating did not alter our consideration of the *140privacy issue. Nor did such a consideration affect our analysis in Payton v. New York, 445 U. S. 573 (1980), in which we reaffirmed the principle that the home is private even though it may be used to harbor a fugitive.
In sum, until today this Court has always looked to the manner in which an individual has attempted to preserve the private nature of a particular fact before determining whether there is a reasonable expectation of privacy upon which the government may not intrude without substantial justification. And it has always upheld the general conclusion that searches constitute at least “those more extensive intrusions that significantly jeopardize the sense of security which is the paramount concern of Fourth Amendment liberties.” United States v. White, 401 U. S. 745, 786 (1971) (Harlan, J., dissenting).
Nonetheless, adopting the suggestion in Place, the Court has veered away from this sound and well-settled approach and has focused instead solely on the product of the would-be search. In so doing, the Court has ignored the fundamental principle that “[a] search prosecuted in violation of the Constitution is not made lawful by what it brings to light.” Byars v. United States, 273 U. S. 28, 29 (1927). The unfortunate product of this departure from precedent is an undifferentiated rule allowing law enforcement officers free rein in utilizing a potentially broad range of surveillance techniques that reveal only whether or not contraband is present in a particular location. The Court’s new rule has rendered irrelevant the circumstances surrounding the use of the technique, the accuracy of the technique, and the privacy interest upon which it intrudes. Furthermore, the Court’s rule leaves no room to consider whether the surveillance technique is employed randomly or selectively, a consideration that surely implicates Fourth Amendment concerns. See 2 W. LaFave, Search and Seizure § 2.2(f) (1978). Although a technique that reveals only the presence or absence of illegal *141activity intrudes less into the private life of an individual under investigation than more conventional techniques, the fact remains that such a technique does intrude. In my view, when the investigation intrudes upon a domain over which the individual has a reasonable expectation of privacy, such as his home or a private container, it is plainly a search within the meaning of the Fourth Amendment. Surely it cannot be that the individual’s reasonable expectation of privacy dissipates simply because a sophisticated surveillance technique is employed.
This is not to say that the limited nature of the intrusion has no bearing on the general Fourth Amendment inquiry. Although there are very few exceptions to the general rule that warrantless searches are presumptively unreasonable, the isolated exceptions that do exist are based on a “balancing [of] the need to search against the invasion which the search entails.” Camara v. Municipal Court, 387 U. S. 523, 537 (1967). Hence it may be, for example, that the limited intrusion effected by a given surveillance technique renders the employment of the technique, under particular circumstances, a “reasonable” search under the Fourth Amendment. See United States v. Place, 462 U. S., at 723 (Blackmun, J., concurring in judgment) (“a dog sniff may be a search, but a minimally intrusive one that could be justified in this situation under Terry”). At least under this well-settled approach, the Fourth Amendment inquiry would be broad enough to allow consideration of the method by which a surveillance technique is employed as well as the circumstances attending its use. More important, however, it is only under this approach that law enforcement procedures, like those involved in this case and in Place, may continue to be governed by the safeguards of the Fourth Amendment.
B
In sum, the question whether the employment of a particular surveillance technique constitutes a search depends on *142whether the technique intrudes upon a reasonable expectation of privacy. This inquiry, in turn, depends primarily on the private nature of the area or item subjected to the intrusion. In cases involving techniques used to locate or identify a physical item, the manner in which a person has attempted to shield the item’s existence or identity from public scrutiny will usually be the key to determining whether a reasonable expectation of privacy has been violated. Accordingly, the use of techniques like the dog sniff at issue in Place constitutes a search whenever the police employ such techniques to secure any information about an item that is concealed in a container that we are prepared to view as supporting a reasonable expectation of privacy. The same would be true if a more technologically sophisticated method were developed to take the place of the dog.
In this case, the chemical field test was used to determine whether certain white powder was cocaine. Upon visual inspection of the powder in isolation, one could not identify it as cocaine. In the abstract, therefore, it is possible that an individual could keep the powder in such a way as to preserve a reasonable expectation of privacy in its identity. For instance, it might be kept in a transparent pharmaceutical vial and disguised as legitimate medicine. Under those circumstances, the use of a chemical field test would constitute a search. However, in this case, as hypothesized above, see supra,, at 134, the context in which the powder was found could not support a reasonable expectation of privacy. In particular, the substance was found in four plastic bags, which had been inside a tube wrapped with tape and sent to respondents via Federal Express. It was essentially inconceivable that a legal substance would be packaged in this manner for transport by a eommon carrier. Thus, viewing the powder as they did at the offices of Federal Express, the DEA agent could identify it with “virtual certainty”; it was essentially as though the chemical identity of the powder was *143plainly visible. See Texas v. Brown, 460 U. S., at 751 (Stevens, J., concurring in judgment). Under these circumstances, therefore, respondents had no reasonable expectation of privacy in the identity of the powder, and the use of the chemical field test did not constitute a “search” violative of the Fourth Amendment.