New York police are testing a hi-tech scanner they say can detect concealed weapons from a distance of about 10 metres.
Commissioner Ray Kelly says trials of the new device started a year ago and are at an advanced stage.
Mr Kelly said the device is a portable box that measures a form of natural energy emitted by people and objects known as terahertz.
If something is obstructing the flow of that radiation, such as a gun, the scanner highlights the object and it appears as a shadowy image, the BBC reports.
This is being seen as a possible alternative to the NYPD's reliance on the policy of stop and frisk, which has raised serious concerns about racial profiling.
Critics say the vast majority of on-the-spot weapons checks target blacks and Latinos.
