Hot Tip

Before I get into the constitutional issues raised by police surveillance using infrared cameras, I'll answer the question that's on everyone's mind: Can they tell when you're having sex?

The answer is yes, under the right circumstances. If you happen to leave your bedroom window open on a warm summer night, it's not safe to assume that what you do with the lights out will go undetected by the authorities.

And if the Supreme Court upholds a 1998 decision by the U.S. Court of Appeals for the 9th Circuit, peeping cops won't even need a search warrant. That's because, according to the appeals court, monitoring someone's home with a thermal imager isn't really a search.

The case, which the Supreme Court recently heard, involves Danny Lee Kyllo, an Oregon man who was arrested for growing marijuana in 1992 after he was incriminated by an Agema Thermovision 210. Pointing the device at Kyllo's home in the middle of the night, a sergeant in the Oregon National Guard detected unusual heat emanating from one wall and from the roof above the garage.

Largely on the strength of these infrared readings, which were interpreted as evidence of the high-intensity lights used to grow pot indoors, a federal agent obtained a warrant to search Kyllo's home, where he found more than 100 marijuana plants. The 9th Circuit ruled that a warrant was not needed for the initial surveillance because it did not constitute a "search" under the Fourth Amendment. "Whatever the 'Star Wars' capabilities this technology may possess in the abstract," the majority said, "the thermal imaging device employed here intruded into nothing."

Danny Kyllo, of course, would disagree. But the court said he did not have a reasonable expectation of privacy concerning the "waste heat" emanating from his home, any more than he would have a right to expect the cops not to notice how much trash he put out on the curb. Indeed, "he took no affirmative action to conceal the waste heat emissions."

The issue, though, is not the heat but the information it conveyed about what was going on inside the house. And since people do not generally expect that observers equipped to record that information will be watching their homes, it is hardly reasonable to insist that they control their infrared emanations if they want to maintain their privacy.

In other words, preventing the escape of "waste heat" is not analogous to drawing the curtains–which, by the way, the Agema 210 can see through. It can also detect people and movement behind glass doors and inside cars with tinted windows.

Even through walls and roofs, infrared readings combined with knowledge of a building's layout can tell observers when residents are engaging in a variety of legal (and heretofore private) activities, such as taking a shower, cooking, washing clothes, using a sauna, or making pottery. Maybe that doesn't sound very impressive. But as Judge John T. Noonan noted in his dissent, citing the technology's current limitations as a reason to exempt it from Fourth Amendment restrictions is similar to suggesting that "if your home was searched by a blind policeman you would have suffered no constitutional deprivation."

Noonan emphasized that infrared monitoring is not like seeing smoke from a chimney or smelling a distinctive odor, which "both depend on unaided human senses." It is more like "a telescope that, unknown to the homeowner, is able from a distance to see into his or her house and report what he or she is reading or writing." In both cases, "the amplification of the senses by technology defeats the homeowner's expectation of privacy."

In a friend-of-the-court brief, the National Association of Criminal Defense Lawyers and the American Civil Liberties Union note that when the Fourth Amendment was written, "physical entries were the principal means of gaining access to concealed information." They argue that "a new device must be constrained by the Constitution whenever it enables officials to learn any confidential information that previously could have been learned only by means of physical intrusion."

The Supreme Court seemed to recognize this point in a 1967 case where it found that the bugging of a telephone booth without a court order was unconstitutional even though it did not involve a physical intrusion. But according to the 9th Circuit's reasoning, the bug should have passed muster because all it did was pick up vibrations from the glass surrounding the phone.