Guess what's behind that wall?
The use of technology that allows the police to "see" inside the homes of suspects has raised privacy questions.
At least 50 US police forces are believed to be equipped with radars that can send signals through walls.
The use of the radar device, known as Range-R, was made public in a Denver court late last year.
It was used by police entering a house to arrest a man who had violated the terms of his parole.
In 2001, the Supreme Court ruled that police cannot use thermal cameras without a warrant, specifically noting that the rule would also apply to radar-based systems that were then being developed.
"The idea that government can send signals through the wall of your house to figure out what's inside is problematic," Christopher Soghoian, principal technologist for the American Civil Liberties Union told USA Today.
"Technologies that allow the police to look inside of a home are among the intrusive tools that police have."