Courts have consistently held that law enforcement agencies cannot surveil private spaces without a warrant, especially houses and other domiciles, whether by wiretap or camera. Police can watch exteriors as part of an investigation, but surveillance inside a home requires a warrant, just as non-consensual entries do. Does that include radar? USA Today’s Brad Heath reports that more than 50 law-enforcement agencies have begun using radar as part of their surveillance, although it’s questionable whether they have been deployed without an entry warrant:

At least 50 U.S. law enforcement agencies have secretly equipped their officers with radar devices that allow them to effectively peer through the walls of houses to see whether anyone is inside, a practice raising new concerns about the extent of government surveillance.

Those agencies, including the FBI and the U.S. Marshals Service, began deploying the radar systems more than two years ago with little notice to the courts and no public disclosure of when or how they would be used. The technology raises legal and privacy issues because the U.S. Supreme Court has said officers generally cannot use high-tech sensors to tell them about the inside of a person’s house without first obtaining a search warrant.

So … do they? Thus far, the answer seems to be yes but. The cases he discusses involve arrests based on existing arrest warrants, including one upheld by the 10th Circuit Court of Appeals. In that case, US marshals arrested a fugitive after first using the radar to determine that someone was inside the residence first. That did not involve a search warrant, however, just the arrest warrant — which would be enough to seize someone inside a residence, although not to do a search beyond what is visible to the naked eye during the process of the arrest. Still, even with the knowledge of the radar search (and an initial lack of disclosure), the judges upheld the conviction and at least implicitly justified the use of radar, even though they predicted it would be a thorny issue in some cases.

It also has some connection to the recent debate over the militarization of domestic law enforcement. Unsurprisingly, this technology emerged from the urban warfare of Iraq and Afghanistan, where troops needed to know where potential ambushes might be staged against them. Heath reports that these systems were intended for both ground and drone use, which raises some questions too about domestic law enforcement as they begin to use drones for their work here. Once local law enforcement has these tools, will they be circumspect about their use — or will this represent yet another pushback on the limits of personal privacy?

The ACLU and the Electronic Frontier Foundation want tougher safeguards on their use:

“The problem isn’t that the police have this. The issue isn’t the technology; the issue is always about how you use it and what the safeguards are,” said Hanni Fakhoury, a lawyer for the Electronic Frontier Foundation. …

“The idea that the government can send signals through the wall of your house to figure out what’s inside is problematic,” said Christopher Soghoian, the American Civil Liberties Union’s principal technologist. “Technologies that allow the police to look inside of a home are among the intrusive tools that police have.”

Everyone wants law enforcement to have the tools necessary to make their job as safe as it can be — within the limits of the Constitution. If that requires radar, then law enforcement should be able to make that case to a judge and get a proper search warrant when needed. I’m not a big fan of the ACLU, but they and EFF are correct here.  It’s not the technology itself that’s the problem, it’s ensuring that its use is limited to necessity. If this comes before the Supreme Court, I’d bet that will be an area of agreement across the ideological divide.