"WASHINGTON — 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"
"Agents' use of the radars was largely unknown until December, when a federal appeals court in Denver said officers had 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 new 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."
http://www.usatoday.com/story/news/2015/01/19/police-radar-see-through-walls/22007615/
"Agents' use of the radars was largely unknown until December, when a federal appeals court in Denver said officers had 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 new 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."
http://www.usatoday.com/story/news/2015/01/19/police-radar-see-through-walls/22007615/