At least 50 law enforcement agencies have secretly equipped officers with radar devices that allow them to peer through walls of houses to see whether anyone is inside, reports USA Today. The practice raises concerns about the extent of government surveillance. Agencies including the FBI and the U.S. Marshals Service began deploying the radar systems more than two years ago with no public disclosure of when or how they would be used. The U.S. Supreme Court has said officers cannot use high-tech sensors to tell them about the inside of a house without first obtaining a search warrant. The radars work like motion detectors, using radio waves to zero in on movements as slight as human breathing more than 50 feet away. They can detect whether anyone is inside of a house, where they are and whether they are moving.
Officials say the information is critical for keeping officers safe if they need to storm buildings or rescue hostages. Privacy advocates and judges have expressed concern about the circumstances in which law enforcement agencies may be using the radars, and the fact that they have so far done so without public scrutiny. In December, a federal appeals court in Denver said officers used one before they entered a house to arrest a man wanted for violating his parole. The judges expressed alarm that agents had used the technology without a search warrant, warning that “the government’s warrantless use of such a powerful tool to search inside homes poses grave Fourth Amendment questions.”