Officers from at least 50 law enforcement agencies have been using a hand-held motion detector device that can penetrate walls and detect human presence - a tactic which has generated controversy.

Some law enforcement agencies have been using a relatively new tool in their crime-fighting arsenal--a hand-held radar device that can “see” through walls.

Reportedly at least 50 U.S. law enforcement agencies including the U.S. Marshals Service and the FBI have been using the device the past two years.

Known as RANGE-R, it sends out highly sensitive radio waves that can penetrate walls and detect the presence of an individual through any minute movement, even their breath, in a 50-foot range.

No visual image of the interior is produced.

Serious concerns have been raised about the legality of its deployment with regards to Fourth Amendment search and seizure rights.

The U.S. Supreme Court has ruled in previous cases that a search warrant must be obtained to use implements such as a ther