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FindLaw Forum: What constitutes an unreasonable search? by Sherry F. Colb FindLaw Columnist Special to CNN.com

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(FINDLAW) -- The U.S. Supreme Court's hearing February 20 on what constitutes an unreasonable search under the Fourth Amendment offered some new twists on an old argument.

The case is Kyllo v. U.S. In it, Danny Lee Kyllo challenges his conviction for growing marijuana in home, contending federal drug task force members violated the Fourth Amendment in January 1992 when they searched his premises in Florence, Oregon, without a warrant.

What makes this case worthy of the high court's attention is the nature of the alleged "search."

The task force enlisted the aid of an Oregon National Guard soldier who used a thermal imaging device to detect heat patterns generated by Kyllo's home. The device revealed that parts of the house were radiating unusually high levels of heat such as those created by high-intensity lights used to cultivate marijuana.

The central question in Kyllo is whether the use of this device constituted a "search" -- a government invasion of a person's "reasonable expectation of privacy." If it did, the task force should have obtained a warrant.

'Search' precedents

The government claims that no "search" occurred, for Fourth Amendment purposes, because the device took its measurements from a public vantage. Kyllo counters that because the thermal detector gave the police information about the inside of a private home, using it was a search.

To put the case in context, consider the sorts of police activity that count as "searches" -- entering a person's house, recording telephone conversations, and opening the trunk of the person's car. So do taking blood or urine samples, frisking someone's outer garments and opening mail.

But not every police investigation is a Fourth Amendment "search." Officers may freely observe whatever the rest of the public can observe. They may, for example, watch people walk down the street, listen to conversations in public, and smell (or have a drug-sniffing dog smell) odors emanating from luggage.

Applying precedents

Heat detection technology might seem to fit neatly within the first group of cases. It detects what most people cannot observe: heat patterns.

On the other hand, the device monitors only heat already outside the house. Just as a person who leaves her home exposes herself to public scrutiny, heat that has escaped the home may be similarly available for public observation.

It would be formalistic to allow either the fact that most people lack heat detection technology, or the fact that the detected heat is outside the house, to decide the case.

The real question is whether we ought to strive to preserve as private what thermal detectors can expose.

Privacy in heat emissions?

During oral argument, the government attorney stated that no one cares about preserving privacy for heat outside his walls. That seems true.

But as Justice Stephen Breyer responded, the expectation of privacy at issue is not in the emanation of heat, but in the revelation to the police, via that heat, of what is going on inside the house.

The deputy solicitor general replied that the device does not reveal what is happening in the house.

Justice David Souter pointed out, though, that the device can show people moving around in darkness. Though the device can sometimes detect human forms and activity, however, it generally cannot, and Kyllo concedes that it did not in his case.

The limits of privacy rights

What about the fact that this device can reveal that marijuana is growing in the house? Kyllo clearly did not want the police to have that information. Is that desire on his part sufficient to give rise to a reasonable expectation of privacy?

In attempting to resolve this question, consider a hypothetical case. Imagine a machine that could give us a list of all places in the country where decomposing corpses are concealed.

The machine could scan the entire United States for corpses, and corpses alone, beep a few times, and then provide a printout of an address for each place in which a decomposing corpse is concealed. Does this machine invade anyone's legitimate expectation of privacy?

The person hiding a corpse in his house -- let us call him "Adam" -- would say, "Yes." But is his privacy claim any more compelling than that of his neighbor -- "Eve" -- who has hidden a corpse in the river and feels invaded when the police expose the river's contents? It is not.

If investigators learn no private facts about Adam or his behavior other than that there is a corpse concealed in his home, in what sense has the corpse detector "searched" him any more than it has Eve?

It is the incidental exposure and revelation of non-criminal information that turns the pure disclosure of crime into an invasion of privacy, a search.

Non-criminal information

In analyzing whether the use of a thermal imaging device ought to count as a "search," we might ask how much this device resembles the corpse detector.

The government says the imaging device reveals nothing about what is going on in the house. But the court might demand greater assurances.

If there is a heat pattern associated with cultivating marijuana, then maybe there are heat patterns associated with legal activities, too.

Could police use the machine to detect, for example, how many people are in the house at any given time? Could they detect whether the people are in separate rooms or together?

If the technology could be desensitized so that it reveals only marijuana cultivation but nothing else, it may be appropriate to allow its use, in that desensitized form alone, without a warrant.

The prospect of technology examining our homes seems inherently frightening, and rightly so. Perhaps someday a thermal detection device will provide what is essentially a moving picture of events occurring inside a person's home.

Use of such a device would surely represent a gross invasion of privacy -- and constitute a "search" that we should hesitate to permit even when police have probable cause and a warrant.

At the same time, however, we should try not to react with irrational prejudice to an unfamiliar technology. The more effectively and precisely the police can separate the guilty from the innocent, the less vulnerable we will be to the incidental burdens of police error.

Probable cause and a warrant are ultimately only imperfect tools for determining where police are most likely to discover crime.

If technology can perfect the tools so that they expose less that is personal, and more that is criminal, it has the potential to increase rather than decrease the privacy of us all.

Sherry F. Colb is a professor at Rutgers Law School in Newark, New Jersey, where she teaches criminal procedure and evidence, among other topics. She has written on Fourth Amendment issues in the Columbia Law Review. Sherry F. Colb is also a FindLaw columnist.

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