Thermal sensors

A thermal-imaging device, often called a FLIR (forward-looking infrared radar), is used to detect activity and movement via heat patterns on the surface of a selected target by identifying temperature differentials. The device provides a visual image of objects that are warmer or cooler than the baseline. A thermal imager is capable of locating a human in the dark from a distance in excess of seven kilometers. Although thermal-imaging devices are incapable of seeing through an object, activity or hot spots may be detected if heat from the activity passes through an intermediate object, such as a window or a porous wall.
Thermal imagers are prized commodities that have been applied in a variety of circumstances. The U.S. Border Patrol uses the device for military surveillance and detection of illegal immigrants. FLIRs have been used to save persons trapped in smoke-ridden buildings as well as many other search-and-rescue operations. The imager has assisted in locating countless individuals, including missing children, lost Alzheimer’s patients, fleeing suspects, and escaped convicts. The devices are often used in drug cases to locate hydroponic laboratories. As a result of the refined sensibility of the equipment, the devices have been used recently to detect and identify emissions and air pollutants that are harmful to the environment.
The usefulness of the technology cannot be denied. These devices allow law enforcement to collect otherwise unavailable information passively without a physical intrusion. Thus, for the most part, the suspect has no knowledge that the equipment has been used. Because thermal imagers operate by observing and recording waste heat radiated through the surface of a structure, concerns were raised that Fourth Amendment privacy protection would be analogized to a garbage search inquiry approved by the Supreme Court in 1988 in California v. Greenwood. The concern centered on the collection of private information without notice, as well as the acquisition of confidential data in areas where privacy is highly protected like within a residence. Although the FLIR technology supposedly cannot penetrate walls, it actually does to a certain extent. Without adequate control, this infrared technology could allow the government to search and survey, violating the right to privacy.
The issue is temporarily resolved by the 2001 Supreme Court decision in United States v. Kyllo. In Kyllo, the litigants debated whether the information retrieved by a thermal imager scan was collected through the wall of a home or abandoned property or from heat emanating from the exterior of the home’s walls. The Court, however, sidestepped that debate and focused its decision instead on how the thermal imager was used under the Katz v.United States two-pronged test. First, did the person have an actual subjective reasonable expecta-tion of privacy? Second, was that expectation one that society was prepared to recognize as reasonable? The Court concluded that Kyllo did have a subjective expectation of privacy in the heat emissions within his home since the technology had the potential of revealing more than the contraband hydroponic marijuana-growing operation. Protected information, such as when the lady of the house was bathing, could also be revealed. Furthermore, the subjective privacy expecta-tion was one that society would be willing to recognize. This latter conclusion was reached on the basis that thermal imagers are not devices commonly avail-able to the public. Hence, the interiors of houses are off limits to any technology, no matter how unobtrusive the technology may be, if the technology is not in general use. This decision offers minimal or temporary protection to privacy advocates since new technology is a continuing phenomenon and more technology is being made available to the public.

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