Kyllo v. United States

Following is the case brief for Kyllo v. United States, 533 U.S. 27 (2001)

Case Summary of Kyllo v. United States:

  • Federal agents used a thermal imaging device outside of Kyllo’s home, suspecting that Kyllo was growing marijuana in his home, which requires use of heat lamps.
  • The device indicated that more heat was emanating from Kyllo’s residence than from neighboring residences.  Using the heat information in conjunction with other facts, the agents obtained a warrant to search Kyllo’s residence.  They discovered that Kyllo was, in fact, growing marijuana in his home.
  • Kyllo moved to suppress the evidence seized from his home before his trial.  The District Court denied the motion.
  • The Ninth Circuit ultimately affirmed the denial.
  • The U.S. Supreme Court reversed, holding that the use of a device that enhanced normal perception to detect heat coming from inside a home was a “search” under the Fourth Amendment, and it was unlawful here because it was conducted without a warrant.

Kyllo v. United States Case Brief

Statement of the Facts:

A U.S. Department of the Interior agent suspected that Danny Kyllo was growing marijuana in his home.  Because indoor marijuana growth requires the use of high intensity heat lamps, the agent used a thermal imager device to detect the amount of heat coming from Kyllo’s home.  The thermal scan of Kyllo’s home took only a few minutes and was conducted by the agent from a car across the street.  The thermal scan revealed that more heat was emanating from Kyllo’s residence than from the other two residences in the triplex in which Kyllo lived.

Based on the thermal scan, tips from informants, and utility bills, the agent obtained a warrant to search Kyllo’s residence.  The search ultimately revealed that Kyllo was running a marijuana growing operation in his residence.

Procedural History:

  • The District Court denied Kyllo’s motion to suppress the evidence seized from his home, and Kyllo then entered a conditional guilty plea.
  • The Ninth Circuit ultimately affirmed the denial of the motion to suppress. The Ninth Circuit reasoned that Kyllo had no reasonable expectation of privacy in the heat emitted from his home, and the thermal scan did not expose any intimate details of Kyllo’s life.
  • The U.S. Supreme Court granted certiorari.

Issue and Holding:

Does the use of a thermal scanning device from a public street, in order to detect the amount of heat coming from a home, constitute a “search” under the Fourth Amendment?  Yes.


The decision of the Ninth Circuit Court of Appeals is reversed and remanded.

Rule of Law or Legal Principle Applied:

The use of sense-enhancing technology to learn information about the interior of someone’s home that could not otherwise have been obtained without physical intrusion into a constitutionally protected area is a “search” for purposes of the Fourth Amendment.


The issue here is the extent to which changes in technology will impact what we as a society deem to be a reasonable expectation of privacy.  It is important not to let police technology erode the privacy guaranteed by the Fourth Amendment.

The fact that the thermal scanner in this case is not in general public use is important.  The thermal scanner allowed police to learn information about what may have been occurring in a person’s home that they would not have learned using their own five senses.  Therefore, use of the thermal scanner is a Fourth Amendment “search.”

The fact that the thermal scan did not reveal private activities occurring in private areas does not take the thermal scan outside the protections of the Fourth Amendment.  Protecting the sanctity of the home was never tied to the quality or quantity of the information obtained.

The case should be remanded so the court can consider whether there was sufficient probable cause for the warrant without the thermal scan information.

Concurring and Dissenting Opinions:

Dissenting Opinion (Stevens):

There is an important difference between “through-the-wall” surveillance, and “off-the-wall” surveillance.  “Through-the-wall surveillance” is clearly a search under the Fourth Amendment.  This case, however, is an example of “off-the-wall” surveillance.  Here, the thermal scanner obtained only information that can be observed from the exterior of the home, which did not infringe on any constitutionally protected interest in privacy.


Kyllo v. United States is an important decision because it confronts the issue of whether the Fourth Amendment can serve as a protector of privacy in a world where technology becomes increasingly intrusive on our private lives.

Student Resources:

Read the Full Opinion

Listen to the Oral Argument