NEW TECHNOLOGIES AND THE FOURTH AMENDMENT: The Trouble With Defining A "Reasonable Expectation Of Privacy"

Editor's Note: Due to technical difficulties, an incomplete version of Barton Aronson's column was posted earlier today on FindLaw's Writ. Here is the correct version.

Recently, the Supreme Court heard oral argument in Kyllo v. United States. To decide the case, the Court will have to decide how society feels about something called thermal imaging - no mean feat, since "society" has never heard of thermal imaging, and therefore has no opinion of it whatsoever. The Kyllo case nicely illustrates the fact that when it comes to the Fourth Amendment generally, and searches conducted using new technology in particular, judges don't have a lot to go on.

Danny Kyllo pled guilty to manufacturing marijuana after the police caught him growing 100 marijuana plants. The police had some scattered information connecting Kyllo to marijuana production, including the fact that his utility bills were unusually high: growing marijuana indoors requires powerful heat lamps. But you can, of course, eat up a lot of electricity without generating intense, focused heat. This is where the thermal imager comes in.

The imager is a fairly crude instrument. It senses different amounts of heat emanating from different parts of a building (your walls, your roof) or different buildings (your house, your neighbor's). It translates that heat into an image in which greater amounts of heat appear lighter and lesser amounts appear darker. The imager doesn't tell the police what's generating the heat, or the precise temperature.

Sure enough, the thermal imager showed unusually high levels of heat emissions from particular parts of Kyllo's home - indicating that he might, indeed, be using the powerful heat lamps required to grow marijuana. All of this information persuaded a judge to issue a warrant, and the police who executed the warrant found Kyllo's marijuana operation.

The Fourth Amendment says that the government cannot engage in "unreasonable" searches of our "persons, houses, papers, and effects," and that search warrants require probable cause. If it's not a search, the police don't need a warrant. If you're growing marijuana on your front lawn, for example, and the police walk by and see it, they haven't conducted a "search" at all. It's only a search if the government somehow invades your privacy.

To decide whether the police have invaded your privacy by conducting a search, courts ask two questions: did the defendant have a personal expectation of privacy, and is society prepared to recognize that expectation as reasonable? We ask the second question because the language of the Fourth Amendment appears to require it, protecting us as it does only against "unreasonable" government activity.

It's the second question that involves judges in an unusual role. To begin with, the Fourth Amendment's use of the word "unreasonable" is remarkable: none of the other rights protected in the Bill of Rights hinges on the reasonableness of the government's conduct.

Freedom of speech is protected - period; the defendant's right to confront the witnesses against him is protected - period; and so on. Of course, courts have grafted limitations onto most of this absolutist language (you can't yell "fire" in a crowded theater), but the Framers themselves only put the "reasonableness" front and center when it came to searches.

A so-called textual approach to the Fourth Amendment is of little help. Eighteenth century dictionaries define the word "reasonable" as nebulously as the dictionaries of today do. Reasonable means reasonable. All other efforts at definition are nothing but lists of synonyms.

An originalist approach is no better, despite recent efforts by some judges to use one. Originalism is a plausible approach only when the language in issue had a widely understood meaning by those who used it. But unlike "due process" or "cruel and unusual punishment," the expression "unreasonable searches and seizures" was not a term of art used by eighteenth century lawyers. Thus, there is no body of writings that shed light on what that phrase meant to the people who used it. What is reasonable has always turned entirely on the specific facts of the matter, and it is simply, well, unreasonable to suggest that the Framers had any different understanding of the word.

The law, of course, is chock full of reasonableness standards. If you're accused of being negligent, for example, the jury will decide whether you behaved as a reasonable person would have behaved. If you defend against assault charges by asserting that you needed to defend yourself, the jury will debate whether your fear of attack was reasonable.

In both of these examples, and countless others, a jury - that is, a stand-in for the community - decides whether some conduct is reasonable. In so doing, the jury will essentially consult itself: what is reasonable is what society says is reasonable; the jury represents society; therefore, anything the jury says is reasonable is so. The Fourth Amendment, perhaps uniquely among the rights safeguarded by the constitution, requires judges to play this role, too.

How do judges intuit society's views on privacy? The way judges usually do things: by analogy. Is thermal imaging more like going through your garbage (which courts have allowed) or more like looking into your window with a high-powered telescope (for which courts generally require a warrant)? These analogies, of course, come from prior Fourth Amendment cases. In other words, to find out what society thinks is reasonable, judges look at what other judges have said society thinks is reasonable.

The limits of this approach are especially acute when Fourth Amendment cases involve unusual technology. Thermal imaging has been around for years, but it's a fair bet that most people have never heard of it, and don't really have an opinion about it. Moreover, the history or availability of technology is not much of a guide to Fourth Amendment opinions. Telescopes have been around forever, and you can buy them in any store, but you still can't use very high-powered ones to peer into house windows without a warrant.

In contrast, consider your telephone calls. For years, the telephone company had no means for detecting what numbers you were dialing. Now, of course, the telephone company knows exactly what numbers you're dialing, and those numbers show up on your phone bill and caller ID devices; as a result, the courts no longer recognize a privacy interest in that information.

Telescopes have been able to snoop into our homes for a lot longer than the phone company has known what numbers we're dialing. How did the courts decide that society has reconciled itself to one technology but not the other? Through their personal experiences and the personal experience of other judges — not exactly how judges are supposed to approach legal questions.

The Constitution usually asks judges to "say what the law is," in Chief Justice John Marshall's famous phrase. Perhaps uniquely, the Fourth Amendment invites judges not to say what the law is, but to breathe in the zeitgeist. It is not at all clear what special tools judges have for doing this, but it is clear — reasonably clear, anyway — that that is exactly what the Fourth Amendment requires. Lucky for us, judges are people, too.