AIT will NOT "alarm from concealed explosives." It MIGHT alarm from SOME poorly-concealed explosives, but it will definitely not alarm from internally-carried explosives (rectally or swallowed), nor will it alarm to the presence of explosives concealed on the soles of the feet. Loren has stated that explosives with carefully feathered edges might also get through, and this seems plausible to me, though unproven AFAIK.

Baggage x-ray scanners with ATR actually do detect guns, though they're not, according to what I've read, setup to detect explosives (trace detection swabs and manual searches are relied on for those). Carry-on x-ray scanners don't even have ATR, so they don't detect anything, either; it's the operator who detects things, by looking at the image on the scanner screen.

WTMDs definitely detect the presence of metal. That is a definite. They identify it as metal. They don't identify which metal, and they don't localize the position of the metal; that must be done with either a manual search or a HHMD. HHMDs will not only detect the presence of metal, but will localize it and tell you exactly where it is on the body.

Even ETD can't actually detect explosives; it merely detects the presence of trace amounts of specific chemicals, which are components of common explosives. In other words, a positive on an ETD test means, "This person has been exposed to glycerine"; whether that glycerine was a component of explosives or a component of hand soap doesn't matter. To determine whether explosives are actually present, the ETD operator conducts a physical search of the person who tested positive for glycerine. Ditto for all of the other chemicals that ETD tests for.

"That would leave us with the WTMD and hand-searches of all carry-on and checked luggage."

DUH. That's exactly what we want! The rest of it is a bunch of smoke and mirrors that does little or nothing to make us any safer or catch bad guys, while actively sucking money and resouces away from equipment and methodologies that might actually have some positive impact on security.

Now, truthfully, I do support the use of ETD technology, including the portals (if they could ever make the darn things work reliably in an airport environment). It's a non-invasive methodology that, while not perfect, is effective when used by properly trained personnel and adds genuine benefit to the process.

AIT, on the other hand, is worse than useless.