The Journal of
Cognitive Liberties

This article is from Vol. 2, Issue No. 3 pages 83-88
All rights reserved worldwide.  ISSN: 1527-3946





 Supreme Court

Limits Police Surveillance

Richard Glen Boire

On June 11, 2001, the U.S. Supreme Court decided a case, Kyllo v. United States, with important implications for cognitive liberty. The case strengthened the degree of privacy given to Americans' homes in the face of new high-tech police surveillance tools. The Center for Cognitive Liberty & Ethics maintains that our own minds must receive at least as much protection as our homes. Below is a summary of the decision.


In an important decision setting a boundary on when police may use certain high-tech surveillance equipment, the US Supreme Court ruled (June 11, 2001) that police must obtain a search warrant before using an infrared heat-detecting device to peer into a person’s home.

The case involved Danny Kyllo, whose home was scanned by police officers using a thermal imaging device. Thermal imagers detect infrared heat radiation, which is not detectable by the naked eye.

After receiving a tip that Mr. Kyllo might be growing marijuana in his home, and learning that his utility bills were relatively high, two police officers drove by Kyllo’s home, scanning it with a Thermovision 210TM device made by Agema Corporation (recently merged with FLIR Systems). The device revealed hot spots consistent with the use of high-intensity lights used to grow plants, including marijuana, indoors. Based on the information from the thermal scan, the informant’s tip, and the utility company, a judge issued a search warrant for Kyllo’s home. The search uncovered an indoor marijuana garden. At issue in the case was whether the use of the thermal imager was a “search” within the meaning of the Fourth Amendment. If use of the device was not a search, then the police can use a thermal imager any time for any reason. But, if scanning a person’s home with such a device is considered a “search” then it would be presumptively unconstitutional for the police to use a thermal imager without first obtaining a search warrant.

The government argued that police use of a thermal imager was not a search because such devices detect “only heat radiating from the external surfaces of the house,” and that such heat “waste” is equivalent to garbage placed on the curb for pickup—something that the Court previously held could be examined by the police without a search warrant.

Kyllo argued that a person’s home is a private place that has traditionally received the highest protection against government searches. Use of the thermal imager to peer through the walls of his home was, he argued, equivalent to the police invading his home and looking around—something they could not do without a search warrant.

In a fascinating opinion, which not only strengthens the privacy protections of the home, but which also has juridical implications for cognitive liberty and autonomy, five of the nine Supreme Court justices sided with Mr. Kyllo, holding that the officers’ use of the thermal imager without a search warrant violated Mr. Kyllo’s Fourth Amendment protection to be secure inside his home.

Writing for the majority, Justice Scalia noted that in the postmodern age, it is possible—and will become increasingly more so—for the police to invade a person’s home without physically entering it. “The question we confront today,” explained Scalia, “is what limits there are upon [the] power of technology to shrink the realm of guaranteed privacy.”

Scalia explained that the Court was making an effort at establishing a rule that would serve to protect Americans' homes from virtual police invasions made possible by a host of high-tech surveillance devices currently on the market, and those yet to come. In a footnote, Scalia briefly outlined some of the new technology that made such a broad rule necessary if the home is to remain a private sanctuary even while Big Brother arms himself with an ever-expanding array of advanced surveillance and policing tools:

The ability to “see” through walls and other opaque barriers is a clear, and scientifically feasible, goal of law enforcement research and development. The National Law Enforcement and Corrections Technology Center, a program within the United States Department of Justice, features on its Internet Website projects that include a “Radar-Based Through-the-Wall Surveillance System,” Handheld Ultrasound Through the Wall Surveillance,” and a “Radar Flashlight” that “will enable law enforcement officers to detect individuals through interior building walls.”

Scalia rejected the government’s argument that the thermal imaging was constitutional because it was limited to detecting hot and cold areas and thus did not detect private or intimidate activities going on in Mr. Kyllo’s home. Scalia drew a firm line at the door to the home: “In the home, our cases show, all details are intimate details, because the entire area is held safe from prying government eyes.” Additionally, Scalia pointed out that a thermal imager could indeed detect intimate details, such as “what hour each night the lady of the house takes her daily sauna and bath,” and that surveillance devices currently under development will surely present even greater threats. With these concerns in mind, Scalia announced that the rule of the case:

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.

While Scalia and the four other justices that joined him should be applauded for setting a limit on the government’s use of privacy-invading electronica, the rule they created is far from perfect.

At the same time that the majority created a bright-line rule that police must get a search warrant before peeking inside of a person’s home with the aid of “sense-enhancing technology,” the majority created a poorly reasoned and difficult to administer “popularity limitation;” namely that the warrantless use of such a device is permitted if that device is also “in general public use.”

Such a popularity limit means that Fourth Amendment protections will become subservient to the marketing prowess of companies that manufacture and sell surveillance technology. On one day, the police must obtain a warrant before using their X-ray glasses, and the next day, no warrant is required because the company inked a deal selling 10,000 X-ray glasses to the General Motors management. “No warrant needed—over 10,000 units sold to consumers!”

As noted by Justice Stevens, who authored the dissenting opinion and was joined by Justices Rehnquist, O’Connor, and Kennedy, the Thermovision 210TM imager used by the police to scan Mr. Kyllo’s home is, itself, a relatively popular device:

The record describes a device that numbers close to a thousand manufactured units; that has a predecessor numbering in the neighborhood of 4,000 to 5,000 units; that competes with a similar product numbering from 5,000 to 6,000 units; and that is “readily available to the public” for commercial, personal, or law enforcement purposes, and is just an 800-number away from being rented from half a dozen national companies” by anyone who wants one.

Besides being an absurd rule, the popularity limit is impossible to apply. At what point, for example, will a new technology be considered “in general public use?” How are police officers expected to make that determination, in order to know whether a search warrant is required?

Despite this major flaw, the majority opinion lays down an important corner stone on the jurisprudential landscape of high-tech police-citizen surveillance:

[w]here, as here, the Government uses a device that is not in general public use, to explore the 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.

This does not mean that the police can never use an advanced thermal imaging device to peek inside someone’s home. It simply, but importantly, means that if the device is not "in general public use," the police must get a judge to authorize their use of the device by signing a search warrant. The practical result, in addition to keeping us all more protected from the secret gaze of police, is that law enforcement agents will have a more difficult time detecting indoor marijuana patches and arresting the naughty gardeners.

The decision in Kyllo is also noteworthy with respect to the breakdown of the normal conservative-liberal teaming of the justices. It was surprising to find Justice Stevens siding with the police and Justice Scalia siding with the marijuana grower. This seems to indicate that traditional alignments within the court are eroding and that the Court’s decisions in the future, especially in the areas of privacy, technology, and individual rights, may not be as predictable as they have been in the past.

The full opinion in the case, including the dissenting opinion, can be read online at:


jclcover1.jpg (4845 bytes)

Learn more about subscribing to the print version