June 12, 2001
Excerpts From Supreme Court Ruling on Limits on Surveillance Technology
By THE NEW YORK TIMES
WASHINGTON, June 11 — Following are excerpts from the Supreme Court's decision today that the police must obtain a warrant before using a heat-sensing device to search for illegal activity in a home. The vote in Kyllo v. United States was 5 to 4. Justice Antonin Scalia wrote the majority opinion, and Justice John Paul Stevens wrote the dissent.
FROM THE DECISION By Justice Scalia
This case presents the question whether the use of a thermal-imaging device aimed at a private home from a public street to detect relative amounts of heat within the home constitutes a "search" within the meaning of the Fourth Amendment. . . .
The Fourth Amendment provides that "the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated." "At the very core" of the Fourth Amendment "stands the right of a man to retreat into his own home and there be free from unreasonable governmental intrusion." With few exceptions, the question whether a warrantless search of a home is reasonable and hence constitutional must be answered no.
On the other hand, the antecedent question of whether or not a Fourth Amendment "search" has occurred is not so simple under our precedent. The permissibility of ordinary visual surveillance of a home used to be clear because, well into the 20th century, our Fourth Amendment jurisprudence was tied to common-law trespass. Visual surveillance was unquestionably lawful because "the eye cannot by the laws of England be guilty of a trespass." We have since decoupled violation of a person's Fourth Amendment rights from trespassory violation of his property, but the lawfulness of warrantless visual surveillance of a home has still been preserved. As we observed in California v. Ciraolo (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."
One might think that the new validating rationale would be that examining the portion of a house that is in plain public view, while it is a "search" despite the absence of trespass, is not an "unreasonable" one under the Fourth Amendment. But in fact we have held that visual observation is no "search" at all — perhaps in order to preserve somewhat more intact our doctrine that warrantless searches are presumptively unconstitutional.
In assessing when a search is not a search, we have applied somewhat in reverse the principle first enunciated in Katz v. United States (1967). Katz involved eavesdropping by means of an electronic listening device placed on the outside of a telephone booth — a location not within the catalog ("persons, houses, papers, and effects") that the Fourth Amendment protects against unreasonable searches. We held that the Fourth Amendment nonetheless protected Katz from the warrantless eavesdropping because he "justifiably relied" upon the privacy of the telephone booth. As Justice Harlan's oft-quoted concurrence described it, a Fourth Amendment search occurs when the government violates a subjective expectation of privacy that society recognizes as reasonable. We have subsequently applied this principle to hold that a Fourth Amendment search does not occur — even when the explicitly protected location of a house is concerned — unless "the individual manifested a subjective expectation of privacy in the object of the challenged search," and "society [is] willing to recognize that expectation as reasonable."
We have applied this test in holding that it is not a search for the police to use a pen register at the phone company to determine what numbers were dialed in a private home, and we have applied the test on two different occasions in holding that aerial surveillance of private homes and surrounding areas does not constitute a search.
The present case involves officers on a public street engaged in more than naked- eye surveillance of a home. We have previously reserved judgment as to how much technological enhancement of ordinary perception from such a vantage point, if any, is too much. While we upheld enhanced aerial photography of an industrial complex in Dow Chemical , we noted that we found "it important that this is not an area immediately adjacent to a private home, where privacy expectations are most heightened."
It would be foolish to contend that the degree of privacy secured to citizens by the Fourth Amendment has been entirely unaffected by the advance of technology. For example, as the cases discussed above make clear, the technology enabling human flight has exposed to public view (and hence, we have said, to official observation) uncovered portions of the house and its curtilage that once were private. The question we confront today is what limits there are upon this power of technology to shrink the realm of guaranteed privacy.
The Katz [v. United States] test — whether the individual has an expectation of privacy that society is prepared to recognize as reasonable — has often been criticized as circular, and hence subjective and unpredictable. While it may be difficult to refine Katz when the search of areas such as telephone booths, automobiles, or even the curtilage and uncovered portions of residences are at issue, in the case of the search of the interior of homes — the prototypical and hence most commonly litigated area of protected privacy — there is a ready criterion, with roots deep in the common law, of the minimal expectation of privacy that exists, and that is acknowledged to be reasonable. To withdraw protection of this minimum expectation would be to permit police technology to erode the privacy guaranteed by the Fourth Amendment.
We think that obtaining by sense-enhancing technology any information regarding the interior of the home that could not otherwise have been obtained without physical "intrusion into a constitutionally protected area" constitutes a search — at least where (as here) the technology in question is not in general public use. This assures preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted. On the basis of this criterion, the information obtained by the thermal imager in this case was the product of a search.
The government maintains, however, that the thermal imaging must be upheld because it detected "only heat radiating from the external surface of the house." The dissent makes this its leading point, contending that there is a fundamental difference between what it calls "off-the-wall" observations and "through-the-wall surveillance." But just as a thermal imager captures only heat emanating from a house, so also a powerful directional microphone picks up only sound emanating from a house — and a satellite capable of scanning from many miles away would pick up only visible light emanating from a house.
We rejected such a mechanical interpretation of the Fourth Amendment in Katz, where the eavesdropping device picked up only sound waves that reached the exterior of the phone booth. Reversing that approach would leave the homeowner at the mercy of advancing technology — including imaging technology that could discern all human activity in the home. While the technology used in the present case was relatively crude, the rule we adopt must take account of more sophisticated systems that are already in use or in development.
The dissent's reliance on the distinction between off-the-wall and through-the-wall observation is entirely incompatible with the dissent's belief, which we discuss below, that thermal-imaging observations of the intimate details of a home are impermissible. The most sophisticated thermal imaging devices continue to measure heat off the wall rather than through the wall; the dissent's disapproval of those more sophisticated thermal-imaging devices, is an acknowledgement that there is no substance to this distinction.
As for the dissent's extraordinary assertion that anything learned through "an inference" cannot be a search, that would validate even the through-the-wall technologies that the dissent purports to disapprove. Surely the dissent does not believe that the through-the-wall radar or ultrasound technology produces an 8-by-10 Kodak glossy that needs no analysis (i.e., the making of inferences). And, of course, the novel proposition that inference insulates a search is blatantly contrary to United States v. Karo (1984), where the police "inferred" from the activation of a beeper that a certain can of ether was in the home. The police activity was held to be a search, and the search was held unlawful.
The government also contends that the thermal imaging was constitutional because it did not "detect private activities occurring in private areas." It points out that in Dow Chemical we observed that the enhanced aerial photography did not reveal any "intimate details." Dow Chemical, however, involved enhanced aerial photography of an industrial complex, which does not share the Fourth Amendment sanctity of the home.
The Fourth Amendment's protection of the home has never been tied to measurement of the quality or quantity of information obtained. In Silverman, for example, we made clear that any physical invasion of the structure of the home, "by even a fraction of an inch," was too much, and there is certainly no exception to the warrant requirement for the officer who barely cracks open the front door and sees nothing but the nonintimate rug on the vestibule floor. In the home, our cases show, all details are intimate details, because the entire area is held safe from prying government eyes. . . .
The judgment of the Court of Appeals is reversed; the case is remanded for further proceedings consistent with this opinion.
It is so ordered.
FROM THE DISSENT By Justice Stevens
There is, in my judgment, a distinction of constitutional magnitude between "through-the-wall surveillance" that gives the observer or listener direct access to information in a private area, on the one hand, and the thought processes used to draw inferences from information in the public domain, on the other hand.
The court has crafted a rule that purports to deal with direct observations of the inside of the home, but the case before us merely involves indirect deductions from "off the wall" surveillance, that is, observations of the exterior of the home. Those observations were made with a fairly primitive thermal imager that gathered data exposed on the outside of petitioner's home but did not invade any constitutionally protected interest in privacy. Moreover, I believe that the supposedly "bright line" rule the court has created in response to its concerns about future technological developments is unnecessary, unwise, and inconsistent with the Fourth Amendment.
There is no need for the court to craft a new rule to decide this case, as it is controlled by established principles from our Fourth Amendment jurisprudence. One of those core principles, of course, is that "searches and seizures inside a home without a warrant are presumptively unreasonable." But it is equally well settled that searches and seizures of property in plain view are presumptively reasonable. Whether that property is residential or commercial, the basic principle is the same: "What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection." That is the principle implicated here.
While the court "takes the long view" and decides this case based largely on the potential of yet-to-be-developed technology that might allow through-the-wall surveillance, this case involves nothing more than off-the- wall surveillance by law enforcement officers to gather information exposed to the general public from the outside of petitioner's home. All that the infrared camera did in this case was passively measure heat emitted from the exterior surfaces of petitioner's home; all that those measurements showed were relative differences in emission levels, vaguely indicating that some areas of the roof and outside walls were warmer than others.
As still images from the infrared scans show, no details regarding the interior of petitioner's home were revealed. Unlike an X-ray scan, or other possible through-the- wall techniques, the detection of infrared radiation emanating from the home did not accomplish "an unauthorized physical penetration into the premises," nor did it "obtain information that it could not have obtained by observation from outside the curtilage of the house."
Indeed, the ordinary use of the senses might enable a neighbor or passerby to notice the heat emanating from a building, particularly if it is vented, as was the case here. . . .
Such use of the senses would not convert into an unreasonable search if, instead, an adjoining neighbor allowed an officer onto her property to verify her perceptions with a sensitive thermometer. Nor, in my view, does such observation become an unreasonable search if made from a distance with the aid of a device that merely discloses that the exterior of one house, or one area of the house, is much warmer than another. Nothing more occurred in this case.
Thus, the notion that heat emissions from the outside of a dwelling is a private matter implicating the protections of the Fourth Amendment (the text of which guarantees the right of people "to be secure in their houses" against unreasonable searches and seizures) is not only unprecedented but also quite difficult to take seriously. Heat waves, like aromas that are generated in a kitchen, or in a laboratory or opium den, enter the public domain if and when they leave a building. A subjective expectation that they would remain private is not only implausible but also surely not "one that society is prepared to recognize as 'reasonable.' "
To be sure, the homeowner has a reasonable expectation of privacy concerning what takes place within the home, and the Fourth Amendment's protection against physical invasions of the home should apply to their functional equivalent. But the equipment in this case did not penetrate the walls of petitioner's home, and while it did pick up "details of the home" that were exposed to the public, it did not obtain "any information regarding the interior of the home." In the court's own words, based on what the thermal imager "showed" regarding the outside of petitioner's home, the officers "concluded" that petitioner was engaging in illegal activity inside the home.
It would be quite absurd to characterize their thought processes as "searches," regardless of whether they inferred (rightly) that petitioner was growing marijuana in his house, or (wrongly) that "the lady of the house [was taking] her daily sauna and bath." In either case, the only conclusions the officers reached concerning the interior of the home were at least as indirect as those that might have been inferred from the contents of discarded garbage, or pen register data, or, as in this case, subpoenaed utility records. For the first time in its history, the court assumes that an inference can amount to a Fourth Amendment violation.
Notwithstanding the implications of today's decision, there is a strong public interest in avoiding constitutional litigation over the monitoring of emissions from homes, and over the inferences drawn from such monitoring.
Just as "the police cannot reasonably be expected to avert their eyes from evidence of criminal activity that could have been observed by any member of the public," so too public officials should not have to avert their senses or their equipment from detecting emissions in the public domain such as excessive heat, traces of smoke, suspicious odors, odorless gases, airborne particulates, or radioactive emissions, any of which could identify hazards to the community. In my judgment, monitoring such emissions with "sense-enhancing technology," and drawing useful conclusions from such monitoring, is an entirely reasonable public service.
On the other hand, the countervailing privacy interest is at best trivial. After all, homes generally are insulated to keep heat in, rather than to prevent the detection of heat going out, and it does not seem to me that society will suffer from a rule requiring the rare homeowner who both intends to engage in uncommon activities that produce extraordinary amounts of heat, and wishes to conceal that production from outsiders, to make sure that the surrounding area is well insulated. The interest in concealing the heat escaping from one's house pales in significance to the "the chief evil against which the wording of the Fourth Amendment is directed," the "physical entry of the home," and it is hard to believe that it is an interest the framers sought to protect in our Constitution.
Since what was involved in this case was nothing more than drawing inferences from off-the-wall surveillance, rather than any through-the-wall surveillance, the officers' conduct did not amount to a search and was perfectly reasonable.
Instead of trying to answer the question whether the use of the thermal imager in this case was even arguably unreasonable, the court has fashioned a rule that is intended to provide essential guidance for the day when "more sophisticated systems" gain the "ability to `see' through walls and other opaque barriers."
The newly minted rule encompasses "obtaining  by sense-enhancing technology  any information regarding the interior of the home  that could not otherwise have been obtained without physical intrusion into a constitutionally protected area  at least where (as here) the technology in question is not in general public use."
In my judgment, the court's new rule is at once too broad and too narrow, and is not justified by the court's explanation for its adoption. As I have suggested, I would not erect a constitutional impediment to the use of sense-enhancing technology unless it provides its user with the functional equivalent of actual presence in the area being searched.
Despite the court's attempt to draw a line that is "not only firm but also bright," the contours of its new rule are uncertain because its protection apparently dissipates as soon as the relevant technology is "in general public use." Yet how much use is general public use is not even hinted at by the court's opinion, which makes the somewhat doubtful assumption that the thermal imager used in this case does not satisfy that criterion. In any event, putting aside its lack of clarity, this criterion is somewhat perverse because it seems likely that the threat to privacy will grow, rather than recede, as the use of intrusive equipment becomes more readily available. . . .
Although the court is properly and commendably concerned about the threats to privacy that may flow from advances in the technology available to the law enforcement profession, it has unfortunately failed to heed the tried and true counsel of judicial restraint. Instead of concentrating on the rather mundane issue that is actually presented by the case before it, the court has endeavored to craft an all-encompassing rule for the future. It would be far wiser to give legislators an unimpeded opportunity to grapple with these emerging issues rather than to shackle them with prematurely devised constitutional constraints.
I respectfully dissent.