When the U.S. Supreme Court considers a case argued last week on the use of thermal-imaging cameras and the right, under the Fourth Amendment, “of the people to be secure in their persons, houses, papers and effects against unreasonable searches and seizures,” they may well turn to a recent Maine decision on the issue. And while the technical aspects of the question, of course, could not have been anticipated in 1791 when the 4th amendment was ratified, the underlying meaning of privacy remains as clear in the current high-tech instance as it did 210 years ago.

U.S. District Judge Gene Carter of Maine recently agreed with most other district judges who have considered whether a warrant is needed before thermal-image devices are used by law-enforcement officers to gather evidence – commonly evidence of large amounts of heat generated by powerful lights used in the indoor cultivation of marijuana. The Maine case centered on arrests in Turner after Maine Drug Enforcement agents from a public street used a Raytheon thermal-imaging camera to detect high levels of heat coming from the upstairs windows of a house there. Judge Carter ruled that it was not reasonable to expect that “waste heat” flowing out of house would be considered private and so no search warrant was needed to look for it. However, he added an interesting footnote.

If it could be shown that the particular thermal-imaging device used in the case could detect movements of persons inside a home, he wrote, “a device of such power would present important questions under the Fourth Amendment.” He concluded that the Raytheon Palm 250, used by the MDEA agents, “is not sufficiently sensitive to detect movements or reveal details from inside a structure.”

Raytheon’s description of its product differs from the judge’s assessment. Its web site says the Palm 250 “offers the same capabilities as military thermal imaging” and “detects slight temperature differences between objects and people in its field of view and uses this information to create real-time thermal landscapes of the area on display.” In the Oregon case expected before the Supreme Court, the thermal imager under consideration, the Agema Thermovision 210, includes a “field of view” that could be inside a house’s windows or glass doors. If an imager can “see” heat sources – people – in darkness through a window, it is monitoring something that falls within society’s reasonable expectation of privacy.

In similar cases, the waste heat from houses has been likened to a person’s garbage, which the government might inspect without violating search laws. But garbage is taken out of a house intentionally while waste heat is the undesirable result of leaky walls, windows and roofs. The heat waves are more like cruder versions of voice-produced sound waves that might be imperceptible to the unaided person, but could be identified by highly sensitive listening devices directly outside the home.

And like voice sound waves overheard by these hypothetical listening devices, the heat waves tell the government what is going on or is likely going on in a home. The heat waves coming out of the second-floor of that home in Turner told the agents what was going there just as specifically as getting a ladder and peering through the window would have.

Courts across the nation don’t see it that way. To them, waste heat is fair game for officers with a thermal imager but no warrant. The fact, however, that the Supreme Court is interested in considering the issue suggests there remains a question to be decided – whether the right to be let alone can also protect against the latest technology.