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Privacy Rights in the Digital Age

Kyllo v. United States, 533 U.S. 27 (2001)

by Ethan P. Fallon

A 5–4 decision, with a majority opinion by Justice Antonin Scalia, in which the U.S. Supreme Court ruled that the use of sense-enhancing technology to obtain information regarding the interior of a home that could not otherwise be available without physical intrusion constituted a search under the meaning of the Fourth Amendment. Applying this rule to the case at hand, the Court held that the use of thermal-imaging technology to measure the heat emanating from inside the home constituted a search within the meaning of the Fourth Amendment.

In this case, agents from the U.S. Department of the Interior became suspicious that marijuana was being grown by Danny Kyllo. Growing marijuana indoors typically requires the use of high-intensity lamps, and the agents sought to determine whether the heat emanating from Kyllo's residence was consistent with the use of such lamps. Thus, the agents used a thermal-imaging device to scan Kyllo's residence. The device was equipped to detect infrared radiation, capable of discerning varying degrees of temperatures.

The scan of Kyllo's home revealed that the roof over the garage and a side wall were relatively hot compared to the rest of the home, as well as being substantially warmer than the neighboring homes. The agents concluded that Kyllo was using high-intensity lamps to grow marijuana in his home. A federal magistrate judge issued a warrant to search Kyllo's home, based on the thermal images, utility bills, and tips from informants. The ensuing search revealed that Kyllo indeed was growing marijuana inside his home, where agents discovered over 100 marijuana plants. Kyllo was subsequently indicted on one count of manufacturing marijuana in violation of federal law.

Kyllo moved to suppress the evidence obtained against him, arguing that his Fourth Amendment rights were violated when agents scanned his home. The district court denied his motion to suppress the evidence, and Kyllo entered into a conditional guilty plea. The Court of Appeals for the Ninth Circuit remanded the case, directing the district court to conduct a hearing regarding the intrusiveness of the thermal-imaging technology.

On remand, the district judge concluded that the thermal-imaging device was a nonintrusive investigative tool and reasoned that the technology did not penetrate walls or windows, nor did it show any intimate details within the home. Accordingly, the district court upheld the validity of the original warrant and reaffirmed its denial of Kyllo's motion to suppress the evidence. The court of appeals affirmed the district court's decision, holding that Kyllo did not demonstrate a subjective expectation of privacy because he did not attempt to conceal the heat emanating from his home. The court of appeals further reasoned that there was no objectively reasonable expectation of privacy because the thermal images did not expose any intimate details.

The U.S. Supreme Court agreed to review the case. The Court first analyzed whether the scan of Kyllo's residence constituted a search within the meaning of the Fourth Amendment. The Court noted that its Fourth Amendment jurisprudence was no longer tied to the concept of trespass but rather that the reasonable expectations of privacy test enunciated in Katz v. United States, 389 U.S. 347 (1967), was controlling. Hence, a Fourth Amendment search occurs only where the government violates a subjective expectation of privacy that society recognizes as reasonable.

The Court acknowledged that the degree of privacy secured by the Fourth Amendment had been affected by technological advances. Thus, for the Court, Kyllo was a determination on what limits the power of new technologies had on minimizing the realm of guaranteed privacy. In answering this question, Justice Scalia underscored that the inside of a home was a constitutionally protected area where individuals retain a reasonable expectation of privacy. To withdraw protection from this basic expectation of privacy would be to permit new technology to erode the privacy guaranteed by the Fourth Amendment. Thus, the Court concluded that sense-enhancing technology used to obtain information regarding the interior of the home that could not otherwise have been obtained without physical intrusion constituted a search under the meaning of the Fourth Amendment. Applying this standard to Kyllo, Justice Scalia held that the thermal-imaging scan of the interior of Kyllo's home was an intrusion into a constitutionally protected area and was therefore a search within the meaning of the Fourth Amendment.

The government argued, however, that the use of thermal-imaging technology should be permitted because thermal scanning detects only heat radiating from the external surface of the home, asserting that there is a significant distinction between off-the-wall observations and through-the-wall surveillance. The Court rejected this argument, concluding that such mechanical interpretations of the Fourth Amendment were unavailing.

The Court also rejected the government's contention that the thermal scans of Kyllo's home were permissible because they did not reveal private activities occurring in private areas. Justice Scalia clarified that the Fourth Amendment's protection of the home has never been tied to the quality or quantity of the information obtained and that all details within the home are intimate and are held safe from “prying government eyes.” Justice Scalia also stated that restricting thermal imaging from gathering intimate details would be impractical in application.

Last, Justice Scalia noted that the Fourth Amendment draws a firm and bright line at the entrance of a home, and that a search of Kyllo's home was presumptively unreasonable in the absence of a search warrant. The judgment of the Court of Appeals was therefore reversed, and the case was remanded to the district court to determine whether the search warrant was supported by probable cause once the thermal images were excluded as evidence.

Justice John Paul Stevens, joined by Chief Justice William Rehnquist, Justice Sandra Day O'Connor, and Justice Anthony Kennedy, dissented from the majority opinion. Justice Stevens opposed the majority's new rule regarding sense-enhancing technology, arguing that it was unnecessary and inconsistent with the Fourth Amendment. Justice Stevens argued that a distinction does exist between through-the-wall surveillance and off-the-wall surveillance. Thus, because the case involved detecting heat emanations off the wall of Kyllo's home, Justice Stevens would hold that no Fourth Amendment search occurred.

Further Reading

1 

Kerr, Orin S. “The Fourth Amendment and New Technologies: Constitutional Myths and the Case for Caution.” Michigan Law Review 102, no. 801 (2004).

2 

McInnis, Thomas N. The Evolution of the Fourth Amendment. Lanham, MD: Lexington Books, 2009.

3 

Simmons, Ric. “From Katz to Kyllo: A Blueprint for Adapting the Fourth Amendment to Twenty-First Century Technologies.” Hastings Law Journal 53 1303 (2002): 000–000.

See also: Constitutional law; Criminal justice (criminal procedure); Fourth Amendment to the U.S. Constitution; Katz v. United States; Search warrants; Supreme Court of the United States

Citation Types

MLA 9th
Fallon, Ethan P. "Kyllo V. United States, 533 U.S. 27 (2001)." Privacy Rights in the Digital Age, edited by Christopher T. Anglim & JD, Salem Press, 2016. Salem Online, online.salempress.com/articleDetails.do?articleName=PRDA_0128.
APA 7th
Fallon, E. P. (2016). Kyllo v. United States, 533 U.S. 27 (2001). In C. Anglim & JD (Ed.), Privacy Rights in the Digital Age. Salem Press. online.salempress.com.
CMOS 17th
Fallon, Ethan P. "Kyllo V. United States, 533 U.S. 27 (2001)." Edited by Christopher T. Anglim & JD. Privacy Rights in the Digital Age. Hackensack: Salem Press, 2016. Accessed May 30, 2026. online.salempress.com.