Kyllo v. United States

533 U.S. 27 (2001)

One-Sentence Takeaway

When Government uses a device, such as a thermal imager, that is not in general public use, to explore details of a private home that would previously have been unknowable without physical intrusion, surveillance is a Fourth Amendment “search” and is presumptively unreasonable without a warrant.


Officers suspected Defendant was growing marijuana plants at his home.  They used a thermal imager to scan the temperature of Defendant’s home and discovered that the roof over the garage and sidewalk was relatively hot compared to the rest of the house.  The officers did not actually enter Defendant’s home during this thermal imaging scanning process.  Based on the thermal imaging results, the officers concluded that Defendant was using lights to grow marijuana plants in his house.

Based on the tips from informants, utility bills, and the thermal imaging, a judge issued a search warrant and the officers found more than 100 plants in Defendant’s home.

The issue before the United States Supreme Court was whether the officer’s scan of Defendant’s home with a thermal imager from a public street constituted a “search” under the Fourth Amendment.  The Court answered in the affirmative.

The Court first summarized its prior decisions on the issue as follows:  “But in fact we have held that visual observation is no ‘search’ at all . . . We held that the Fourth Amendment nonetheless protected Katz [in Katz v. United States] 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.'”

The Court ruled that the use of the thermal imager constituted “search” in this case.  The Court explained, “[w]e 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.”

Since the thermal imager was used on Defendant’s home before the officers had obtained a warrant, the Court further held that the warrantless “search” was “presumptively unreasonable.”

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