Thermal Imaging

As for case law, the United States Supreme Court case of Kyllo v. U.S. speaks directly to the question that you have presented.  The facts of the case are set forth below:

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, in violation of 21 U.S.C. § 841(a)(1). He unsuccessfully moved to suppress the evidence seized from his home and then entered a conditional guilty plea.ⁱ

Kyllo’s case was eventually appealed to the United States Supreme Court.  The issue before the court was whether the use of the thermal imaging device to detect levels of heat is a search within the meaning of the Fourth Amendment.

The Supreme Court held “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.”ⁱⁱ

In the case, the government argued that the scan only detected heat that emanated from the home and not the “intimate details” of the interior of the home.  However, the court held further that any information from the home that cannot be obtained without physical entry or sophisticated equipment, such as a thermal imager that is not readily available to the public, is considered “intimate details” of the home.  Therefore, the police needed a search warrant to scan the home using a thermal imager.

Policy considerations that law enforcement agencies can take from this case are relatively straightforward.  Particularly, policy should dictate that entry into private premises to arrest a person or search for evidence must be predicated on (1) a warrant (search or arrest), (2) consent, or (3) exigent circumstances.  Further, if a thermal imaging device is going to be used to facilitate a search for evidence, officers should first obtain a search warrant prior to use of the device.