Noisy, you're probably lucky Im probably the only member of security staff at our airport that reads PPRuNe! Otherwise your discovery would probably get stripped down! But I'll keep my mouth shut for a small fee,
As for XRay screening; it doesnt "detect" anything, just gives us an Xray image of the bag/item in the tunnel. Organic material is orange, inorganic material (such as metal) is blue, and a mix of the two is green. The AMD (Archway metal detector) is whats hunting for metal of course.