[The Cajun]

Yup, I knew they were somewhere in the THz range, but was wondering what particular frequency or band of frequencies in the THz range they were looking at.
Wouldn't want any interference on those frequencies :)
Was also wondering if it is strictly passive or are they looking for some type of resonance associated with a THz signal they generate......Just wondering again.

[coloradan]

There exist both passive and active devices. People are warm and emit T-rays merely by being blackbody radiators, whereas a colder gun doesn’t emit so many themselves, and possibly also reflects the less-intense T-rays coming from the sidewalk and surroundings. In which case the gun looks dark. They go through clothes. Active sensors are basically like radars, looking for reflections from metal, in which case guns would look bright. Then again, if you had a bunch of aluminum-foil silhouettes peppered about your undershirt and pants, you could probably detect the car with such a sensor in either case, because the occupants of said car would probably really, really, want to talk to you.