The lightweight handheld unit uses high frequency microwaves to see through clothes and pick up "reflections" of concealed guns or knives from a distance of several metres.

Intelligent software then interprets the images and only alerts officers to potential weapons - clearly distinguishing between everyday objects like keys and mobile phones.

It is hoped the scanner will reduce the number of attacks on officers who will no longer need to perform a risky stop and search to detect weapons.

Officers will also be able to remain at a safe distance and call for back-up before confronting armed criminals.

Graduating midshipmen of the U.S. Naval Academy in Annapolis are being told in writing to leave at home or in their vehicles all "ceremonial swords" and anything else "that might be considered a weapon or a threat by screeners" for Friday's outdoor commencement ceremonies featuring an address by President Barack Obama.

Inside the Beltway has obtained the academy's list of prohibited items for this years graduation exercises, which, besides ceremonial swords, includes umbrellas.

Yes, cell phones and texting are still allowed.