Dozens of law enforcement agencies in the United States have been outfitted with Doppler radar devices that allow officers to observe people through the walls of their own homes — raising concerns that the devices can be used to violate Fourth Amendment protections.

One popular handheld version of the technology is called the Range-R, produced by New York-based defense contractor L-3 Communications. L-3’s marketing materials promise that the Range-R is sensitive enough to detect a breathing (but otherwise motionless) person on the other side of a 12-inch-thick brick or concrete wall 50 feet away.

According to a Jan. 20 piece in USA Today, L-3 says it has sold about 200 of the devices, at a price of $6,000 each, to about 50 law enforcement agencies. Among them is the United States Marshals Service, which federal records show has spent $180,000 on Range-Rs.

Though it lacks the capability of showing a visual image, the Range-R’s display indicates whether a living person is detected and how far away that person is. Other similar devices are even more sophisticated, like the RadarVision2 — developed by the Alabama-based company Time Domain — which can show how many people are behind a given wall, where they are and whether they are moving. Still other models can be attached to aerial drones and unmanned ground vehicles.

The radar devices, used by soldiers on the battlefield to mitigate the risk of ambushes, are essentially adaptations of military technology. Yet their use in the civilian context was largely unknown before last December, when the U.S. Court of Appeals for the 10th Circuit, in Denver, revealed that one of the devices had been used by police in Wichita, Kan., without a search warrant when they found and arrested Steven Denson inside his own home for violating the conditions of his parole.

“It’s obvious to us and everyone else in this case that the government’s warrantless use of such a powerful tool to search inside homes poses grave Fourth Amendment questions,” the decision read. “New technologies bring with them not only new opportunities for law enforcement to catch criminals but also new risks for abuse and new ways to invade constitutional rights.”

Some privacy advocates believe the police use of a Range-R or similar device without a warrant amounts to “unreasonable searches and seizures,” a violation that the Fourth Amendment is meant to protect against. In fact, the U.S. Supreme Court ruled in 2001, in Kyllo v. United States, that when the government “uses a device that is not in general public use, to explore details of a private home that would previously have been unknowable without physical intrusion, the surveillance is a Fourth Amendment ‘search,’ and is presumptively unreasonable without a warrant.” Later, in the 2013 case Florida v. Jardines, the generally right-wing Justice Antonin Scalia wrote that at the Fourth Amendment’s “very core” is “the right of a man to retreat into his own home and there be free from unreasonable governmental intrusion.”

Nathan Freed Wessler, a staff attorney with the American Civil Liberties Union’s Speech, Privacy and Technology Project, told Truthdig that “there are circumstances when [the device] could be used consistent with the Fourth Amendment. But, he added, “it is absolutely crucial that law enforcement has a proper warrant and limits its use to only gathering information permitted by that warrant. It’s not that hard [to obtain the warrant] if police have probable cause and have a good reason to conduct the search.”

On the other hand, Wessler said, it is important for police to ensure their own safety — by being aware of what is behind the wall of a room before they enter it, for instance — but it is also important for them to do that in a way that does not violate constitutional rights. “It’s important that as new surveillance technologies develop, they don’t leave the Fourth Amendment behind,” he said.Devices that alert police to the presence of a person behind a wall may seem harmless because they do not identify the person being observed, but newer technologies are being developed that could soon give authorities a clearer image of their targets.

Predator drones equipped with heat sensors, sophisticated radar and powerful cameras have already been used by U.S. agencies for tracking criminals who were outside of an investigator’s line of sight. The Massachusetts Institute of Technology has developed a system, called WiTrack, that uses radio signals to obtain precise 3-D motion-tracking data through walls. And a portable device called the Xaver 800, according to its Israel-based developer Camero, is capable of creating a 3-D image of objects behind walls. The company’s CEO Aharon Aharon has said it has sold the device to militaries and police forces around the world.

It is not known whether the U.S. military or any U.S. police departments possess technology that can identify someone on the other side of a wall, but it seems likely that if they do not have such technology now that they will be able to obtain it in the near future.

Both federal courts and privacy advocates already believe that the Fourth Amendment is at risk of being violated by radar devices that can tell only whether someone is home and not who they are. But constitutional protections are obviously at further risk if law enforcement agencies can tell precisely who is behind a wall and what they are doing, without having to obtain a warrant to get that information. Consequently, the United States may be entering an era when the term “transparency” takes on a new, sinister meaning.

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