Kyllo v. United States (2001)

Supreme Court of the United States

Danny Lee Kyllo v. United States 

Decided June 11, 2001 — 533 U.S. 27 

Justice SCALIA delivered the opinion of the Court. 

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. 


In 1991 Agent William Elliott of the United States Department of the Interior came to suspect that marijuana was being grown in the home belonging to petitioner Danny Kyllo, part of a triplex on Rhododendron Drive in Florence, Oregon. Indoor marijuana growth typically requires high-intensity lamps. In order to determine whether an amount of heat was emanating from petitioner’s home consistent with the use of such lamps, at 3:20 a.m. on January 16, 1992, Agent Elliott and Dan Haas used an Agema Thermovision 210 thermal imager to scan the triplex. Thermal imagers detect infrared radiation, which virtually all objects emit but which is not visible to the naked eye. The imager converts radiation into images based on relative warmth—black is cool, white is hot, shades of gray connote relative differences; in that respect, it operates somewhat like a video camera showing heat images. The scan of Kyllo’s home took only a few minutes and was performed from the passenger seat of Agent Elliott’s vehicle across the street from the front of the house and also from the street in back of the house. The scan showed that the roof over the garage and a side wall of petitioner’s home were relatively hot compared to the rest of the home and substantially warmer than neighboring homes in the triplex. Agent Elliott concluded that petitioner was using halide lights to grow marijuana in his house, which indeed he was. Based on tips from informants, utility bills, and the thermal imaging, a Federal Magistrate Judge issued a warrant authorizing a search of petitioner’s home, and the agents found an indoor growing operation involving more than 100 plants. Petitioner was indicted on one count of manufacturing marijuana. He unsuccessfully moved to suppress the evidence seized from his home and then entered a conditional guilty plea.

The Court of Appeals for the Ninth Circuit remanded the case for an evidentiary hearing regarding the intrusiveness of thermal imaging. On remand the District Court found that the Agema 210 “is a non-intrusive device which emits no rays or beams and shows a crude visual image of the heat being radiated from the outside of the house”; it “did not show any people or activity within the walls of the structure”; “[t]he device used cannot penetrate walls or windows to reveal conversations or human activities”; and “[n]o intimate details of the home were observed.” Based on these findings, the District Court upheld the validity of the warrant that relied in part upon the thermal imaging, and reaffirmed its denial of the motion to suppress. A divided Court of Appeals initially reversed, but that opinion was withdrawn and the panel (after a change in composition) affirmed, with Judge Noonan dissenting. The court held that petitioner had shown no subjective expectation of privacy because he had made no attempt to conceal the heat escaping from his home and even if he had, there was no objectively reasonable expectation of privacy because the imager “did not expose any intimate details of Kyllo’s life,” only “amorphous ‘hot spots’ on the roof and exterior wall.” We granted certiorari.  


“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 whether or not a Fourth Amendment “search” has occurred is not so simple under our precedent….but the lawfulness of warrantless visual surveillance of a home has still been preserved. As we observed in California v. Ciraolo, 476 U.S. 207 (1986), “[t]he 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.” 

***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. *** 

We have said that the Fourth Amendment draws “a firm line at the entrance to the house.” That line, we think, must be not only firm but also bright—which requires clear specification of those methods of surveillance that require a warrant. While it is certainly possible to conclude from the videotape of the thermal imaging that occurred in this case that no “significant” compromise of the homeowner’s privacy has occurred, we must take the long view, from the original meaning of the Fourth Amendment forward. 

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. 


Justice STEVENS, with whom THE CHIEF JUSTICE, Justice O’CONNOR, and Justice KENNEDY join, dissenting. 

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. “‘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 “take[s] 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. Additionally, any member of the public might notice that one part of a house is warmer than another part or a nearby building if, for example, rainwater evaporates or snow melts at different rates across its surfaces. 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 are 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 (emphasis added)) 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.’” 



Notes, Comments, and Questions  

The Kyllo majority reasoned in 2001 (in a case about police conduct that occurred in 1991) that the use of thermal imaging constituted a search because the technology was “not in general public use.”  

Today, however, the general public has many uses for thermal imaging, from HVAC performance testing to hunting to wildlife rescue to evaluating the performance of kitchen devices. 

Agema Infrared Systems, the Swedish corporation that manufactured the “Agema Thermovision 210” at issue in Kyllo, was acquired by FLIR Systems Inc. in 1998. Headquartered in Oregon, FLIR now sells a $200 thermal imaging camera (the “FLIR ONE”) that can attach to a smartphone, with fancier versions available for higher prices.  According to the FLIR product page, one can use the FLIR ONE to “[f]ind problems around the home fast, like where you’re losing heat, how your insulation’s holding up, electrical problems, and water damage – all of which are point-and-shoot easy to find.” It also suggests, “See in the dark and explore the natural world safely with the FLIR ONE. Watch animals in their natural habitat and even use it to find your lost pet … or what they might have left behind in the yard.” Another suggested use from the advertisement: “Detecting tiny variations in heat means that you can see in total darkness, create new kinds of art, and discover new things about your world every day… or help your child with their science fair experiment.” 

Consider a police officer who uses such a device to investigate a suspected drug-grower’s home.  He sees images consistent with growing drugs. He shows the images to a judge, who grants a search warrant. Officers find drugs in the house, and prosecutors have charged the owner with drug crimes. Search or no search? Why or why not? 

In January 2020, the City Counsel of Bessemer, Michigan voted to purchase “an odor-detecting device as a means of addressing growing complaints about marijuana odor.” The device is called a “Nasal Ranger,” and the company that sells it describes it as “the ‘state-of-the-art’ in field olfactometry for confidently measuring and quantifying odor strength in the ambient air.” According to St. Croix Sensory, Inc., “The portable Nasal Ranger Field Olfactometer determines ambient odor Dilution-to-Threshold (D/T) concentration objectively with your trained nose.” If a Bessmer police officer stands on a public sidewalk and uses the Nasal Ranger to detect marijuana odors emanating from a house, is that a search? Why or why not? 

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