Most of the courts have decided that targeting a building with a thermal imager is not a search under the Fourth Amendment.10 United States v. Penny-Feeney11 was one of the first cases to consider the matter. The court's reasoning has influenced many other courts on the issue.
No Subjective Expectation of Privacy in "Waste Heat" Using the Katz analysis, the district court concluded that the defendants had no subjective or actual expectation of privacy in the area scanned by the police with the FLIR. The court said that FLIR is limited to "detecting differences in temperature on the surface of the object being observed," and "did no more than gauge and reflect the amount of heat that emanated"12 from the defendants' house. In other words, the FLIR registered only heat escaping from the defendants' house. The court described this escaping heat as waste heat, or "abandoned heat,"13 because the defendants had not tried to prevent its escape. Indeed, they used fans to vent the heat to the outside, voluntarily exposing it to the public. They never attempted "to impede its escape or exercise dominion over it."14
Under these circumstances, the court concluded that the defendants did not have an actual or subjective expectation of privacy in the waste heat. Consequently, the first prong of the Katz case was not satisfied: There was no actual expectation of privacy, so there was no search under the Fourth Amendment that would require a warrant.
Expectation of Privacy Not Objectively Reasonable The court went on to say that even if the defendants had an actual expectation of privacy in this waste heat, it is not an expectation that society is willing to accept. In other words, the defendants could not satisfy the second prong of the Katz test. The court compared heat vented to the outside to trash left for collection on a public street. The Supreme Court has said that garbage bags left for pickup generally are known to be accessible to all manner of animals and people while awaiting the trash collector. In addition, the trash is voluntarily given to trash collectors, who may handle it in any fashion they choose, including giving it to government agents. Therefore, any actual expectation that the garbage will be private is not objectively reasonable.15 By analogy, the court reasoned that waste heat is like trash: Any expectation of privacy in waste heat is objectively unreasonable because individuals may do what they want with it once it is exposed to the public.
Sense-Enhancing Technology Not Overly Intrusive The Penny-Feeney court did not consider the fact that waste heat can only be detected with a FLIR, and not the naked eye, to be legally significant. It relied upon several Supreme Court cases approving the warrantless use of "extrasensory, nonintrusive equipment, such as the FLIR" to investigate people and objects: United States v. Knotts16 (a beeper placed in a container), United States v. Place17 (use of a drug detection dog), and Smith v. Maryland18 (use of a pen register). The court thought the analogy to the use of a drug detection dog was the strongest, citing United States v. Solis.19 Like marijuana odor emanating from a package, Penny-Feeney expected the heat to leave the garage because she deliberately vented it to the outside. Moreover, the court concluded that the use of FLIR by police, like the use of a dog in Solis, was inoffensive because it did not embarrass the defendants or involve a search of their persons. In addition, heat and odor emanations are physical facts indicating a possible crime, not protected communications between people. Finally, the use of the helicopter to aim FLIR at Penny-Feeney's house was deemed lawful under California v. Ciraolo20 and Florida v. Riley21 because the police remained in navigable airspace, and the observation was physically nonintrusive because there was no "invasion of the home or curtilage."22
The Court's Conclusion The Penny-Feeney court concluded that the police did "no more than aim a passive infrared device at defendant's home from an aerial vantage point for the purpose of detecting disposed waste heat on the exterior of the house. No intimate details connected with the use of the home or curtilage were observed and there was no undue noise, no wind, dust, or threat of injury."23 In other words, there was no search within the meaning of the Fourth Amendment.
The majority of courts that have considered the use of thermal imagers have adopted the Penny-Feeney result but have employed slightly different analytical reasoning. One court reasoned that whether a subject takes no steps to prevent heat from escaping or actively vents it outside, both actions demonstrate a "lack of concern for the heat."24 Another court found that from the "balance of the evidence," the defendant had a subjective expectation of privacy because he concealed his growing operation in an underground structure; however, the court decided his expectation was objectively unreasonable.25 All courts upholding the warrantless use of thermal imagers have agreed on the importance of two factors: the lack of a physical intrusion into the targeted area and the scanned image's lack of intimate detail.
