US law enforcement agencies quietly introduce radars that let you see inside houses without a search warrant

Use of the sensors were largely unknown until they cropped up in the report of an arrest over a parole violation in Denver in December

(USA Today)

Radar devices that allow for the detection of movement through walls have been deployed by at least 50 US law enforcement agencies including the FBI and US Marshals, it has emerged, adding to mounting questions about the extent of government surveillance.

Range-R Radar Systems were given to officers with little notice to the courts and no public disclosure of how they would be employed, according to USA Today, despite the US Supreme Court having said that high-tech sensors cannot be used to gather information about the inside of someone's home.

Though the devices can only monitor movement, they are capable of picking up a human breath from over 50 feet away and let officers learn information they would normally need a search warrant for.

The sensors were designed for use in Iran and Afghanistan (Picture: Getty)

Officials say that they are vital in minimising casualties when buildings are stormed, but their nature, along with the furtive way they were introduced, has angered privacy advocates and judges.

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

Designed for use in Afghanistan and Iraq, the sensors were discovered to have been used when officers went to arrest a Denver man for violating his parole in December, though federal contract records show the Marshals Service buying them in 2012.

Judges were alarmed that the sensors were being used without a search warrant, saying that "the government's warrantless use of such a powerful tool to search inside homes poses grave Fourth Amendment questions."