As we near the beginning of the twenty-first century, technology employed by law enforcement in America's war on drugs has advanced rapidly. One example of this advancement is the Forward Looking Infrared (FLIR) device, which detects differences in surface temperature within an enclosed structure. This device enables police officers, for example, to detect signs of a marijuana growth operation inside a building without physically entering.

While several courts have upheld the use of this device without a warrant on private residences, claiming that it is like constitutionally permissible canine-sniff or garbage searches, these analogies are not convincing. Unlike a garbage search, defendants experiencing an FLIR-device search do not voluntarily emit the heat this equipment detects, cannot foresee this kind of search on their homes, and cannot avoid this form of detection. Canine-sniff searches are not analogous because they have a unique nature that does not properly relate to FLIR-device searches. Because these analogies to constitutionally permissible searches are not convincing, the use of an FLIR device without a warrant to search a private residence violates a defendant's constitutional right of privacy within his own home.

An FLIR device detects differences in the surface temperature of targeted objects. The FLIR device highlights man-made heat as a white color and cooler temperatures in shades of gray. The device can detect a human form through a window when the person is leaning against a relatively thin barrier such as a curtain or a plywood door. The device is particularly useful not for detecting general heat loss, but for identifying distinguishable heat signatures inside a closed structure. This makes the device an effective search tool for police investigating marijuana growth operations, as it can detect the unique heat patterns emitted by these operations.

The Fourth Amendment provides that "[t]he right of the people to be secure in their persons, houses, papers, and other effects, against unreasonable searches and seizures, shall not be violated."[1] In Katz v. United States, the Supreme Court set forth a two-pronged test for determining whether a search without a warrant violates a defendant's legitimate expectation of privacy.[2] To be protected, the defendant must have a subjective expectation of privacy, and that expectation must be one that society is prepared to acknowledge as reasonable.[3]

The Supreme Court has also said that people have a reasonable expectation of privacy in their own homes.[4] In fact, homes enjoy a special status in federal constitutional jurisprudence. The Supreme Court has said that "[t]he right of a man to retreat into his own home and there be free from unreasonable government intuition [stands at the] very core [of the Fourth Amendment]."[5] Thus, as defendants in their homes are given the most protection under the Fourth Amendment, residential searches using FLIR devices without a warrant must be closely scrutinized.

Recently the Supreme Court found that the monitoring without a warrant of an electronic beeper inside a private residence, where the beeper was not observable to the naked eye, violated the Fourth Amendment.[6] "For the purposes of the [Fourth] Amendment, the result is the same [as for a physical search without a warrant] where, without a warrant, the Government surreptitiously employs an electronic device to obtain information that it could not have obtained by [unaided] observation from outside the curtailage of the house."[7] Thus, the monitoring of the beeper while it was inside the residence infringed on the homeowners' reasonable expectation of privacy and violated the Fourth Amendment.

Compared to the monitoring of a beeper within a residence, the use of an FLIR device, which can reveal the specific location of a heat source within an enclosed residence, is at least as intrusive. While monitoring heat differentials within a residence does not provide the equivalent of a photographic image, it may be intrusive if it ". . . reveal[s] a critical fact about the interior of the premises that the Government is extremely interested in knowing and that it could not have otherwise obtained without a warrant."[8] An FLIR device certainly can give a government agent critical information regarding a marijuana growth operation that could not be otherwise obtained without a warrant or without observation of the house's exterior. For this reason, using an FLIR device is just as intrusive under the Fourth Amendment as the monitoring of a beeper.

A major argument in favor of allowing an FLIR-device search without a warrant is that defendants do not have a privacy interest in the abandoned heat that this device detects. In United States v. Penny-Feeney, the court held that the use of an FLIR device was not a search because the device only exposed "heat waste" or "abandoned heat," in which the defendant had no legitimate expectation of privacy.[9] The court reasoned that the defendant voluntarily vented the heat waste observed by the police using the FLIR device.[10] The court concluded that this heat waste was no different than garbage placed outside by a defendant for collection, in which the Supreme Court has held there is no reasonable expectation of privacy.[11]

The analogy between garbage left on a curbside and heat radiating from a residence, however, is not very strong or convincing. First, it is difficult to say one voluntarily and actively vents heat in the same way one disposes of garbage. Heat, unlike garbage, leaves a defendant's home without any active participation on the defendant's part. While the Penny-Feeney court emphasized that heat was leaving the defendant's home from a vent to the outside, an FLIR device is used to detect heat within the home and not heat leaving a home through a vent.[12]

Second, a police search of one's garbage is much more foreseeable than the use of an FLIR device to detect heat in one's house. In approving garbage searches in Greenwood, the Supreme Court emphasized that a defendant who places garbage out on a curb assumes the foreseeable risk that other people, children, or animals could discover and seize the contents of the garbage.[13] In contrast, no one would expect that others would use an FLIR device to look into their home and detect heat waste. The Court in Greenwood also pointed out that one can avoid the risk that private information will be detected in garbage by not placing this information in the garbage at all.[14] However, a person cannot choose not to discard heat waste, and thus cannot purposely avoid detection by an FLIR device in the same way.

Finally, garbage searches are not aimed at disclosing details about the interior of a home while the use of an FLIR device is. Because the device can produce images of a house's interior that would not be obtainable through a normal external search, it allows government agents to intrude into a defendant's home. This act is prohibited by the Fourth Amendment because an individual has a legitimate privacy interest in a residential "location not open to visual surveillance."[15] For these reasons, the garbage search analogy does not support the constitutionality of an FLIR-device search without a warrant.

Another major, but unsatisfactory, argument in favor of allowing an FLIR-device search without a warrant is that it is much like a constitutionally permissible canine-sniff search. The Penny-Feeney court found that heat emanations detected by infrared are similar to odor emanations detected by trained dogs.[16]

The analogy that canine-sniff searches are like FLIR-device searches is poor because the Supreme Court has emphasized that canine-sniff searches are sui generis because of the way they obtain evidence and the limited nature of the information they discover.[17] In United States v. Place, the Court found that canine-sniff searches did not violate expectations of privacy because they were limited in scope and not intrusive.[18]

While one could argue that FLIR-device searches are also limited in scope and not intrusive, the Court's reasoning for allowing canine-sniff searches does not translate to FLIR-device searches. The Court held that canine-sniff searches were not intrusive because they do not require luggage to be opened in a public place, exposed to public view, and searched by police.[19] This argument regarding searches in public places does not apply to a search of an individual's private residence. This distinction is important because of the heightened privacy expectation connected with private residences.[20]

The Court's comments on the limited scope of canine-sniff searches also do not apply to FLIR-device searches. The Court stated that canine-sniff searches are limited because they can only detect the presence or absence of narcotics.[21] In contrast, FLIR-device searches can detect anything giving off heat within a residence. Thus an FLIR-device search is not nearly as limited in scope as a canine-sniff search. For these reasons, the argument that an FLIR-device search is like a constitutionally permissible canine-sniff search is not convincing.

While it does take time for the law to catch up with new forms of surveillance technology, no analogy to constitutionally permissible police searches can properly be made to residential searches using an FLIR device. The Supreme Court has established that individuals have a heightened interest in privacy while in their homes, and analogies to constitutionally permissible garbage and canine-sniff searches, while not completely misguided, do not justify an invasion of this interest through the use of an FLIR device without a warrant. An FLIR search does not have the volitional or foreseeable aspects of a garbage search, nor does it share the unique nature of a canine-sniff search. Though FLIR technology is an exciting advance for law enforcement, courts must act responsibly and require a warrant in conjunction with its use for home searches. If courts do not exercise this care, the special protections to privacy in the home established by the Supreme Court will ultimately be hollowed out and laid to waste.