New radar equipment allows police officers to figure out what's going on inside a person's home, triggering concerns among privacy advocates. 

The radar device gives law enforcement officers the power to detect even the slightest motion on the other side of a wall.

The device (pictured below) does not allow the user to literally see a person on the other side.

USA Today reports:

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.

The radars work like finely tuned motion detectors, using radio waves to zero in on movements as slight as human breathing from a distance of more than 50 feet. They can detect whether anyone is inside of a house, where they are and whether they are moving.

[...]

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."

Judge Andrew Napolitano reacted on Fox Business Network, saying one would think that a search warrant would be needed for this type of intrusion. 

Napolitano explained that the government argues no warrant is needed as long as no evidence gained from these devices is used in a prosecution.

He countered, though, that the Fourth Amendment protects against all intrusions by the government, not just criminal prosecutions. 

Napolitano said that possible hostage situations are one of the reasons that the government will give on why this technology should be used. 

"Unfortunately that purpose goes away when they want to use it for other reasons. The Constitution prohibits fishing expeditions!" he said, expressing concern that once an exception is made for hostage situations, more and more exceptions will follow.

Napolitano added that if this technology is going to be used, our elected officials should at least get to vote on it, which has not happened. 

"We learned about this last week when a couple of ex-FBI agents happened to mention it to someone in the press," he said.

Watch his full analysis above and his answers to various scenarios posed by Stuart Varney.