I actually wrote a paper for my "Image Processing for Homeland Security Applications" class on the subject of these new scanners that are in development to detect concealed bombs/weapons. You'd be surprised how accurate the newer millimeter-wave detection systems are at decent range and with low power constraints. Some of the active ones actually create impressive 3D images, and can even use the electromagnetic resonance of an object to determine what the object is made of.
Problem is they are possible to foil, especially the passive systems mentioned in the OP. There are also a few health risks involved that would need to be worked out first.
And it's Killer Angel... as in the book