Discussion on:

Hitachi's boarding gate detects explosives as you pass through

If it screens for traces left on a person handling the explosives, it doesn't sound like much of a screen to me. Someone else can do all the handling, package the explosive in a sealed package and then attach it to a suicide terrorist who would wear the package and pass undetected as I understand what they say the system will do.

This device is effective at picking up conventional explosive residue. Unfortunately it will not pick up unconventional explosive compounds, nor will it pick up sealed conventional explosives which the boarder did not handle, be they a surrogate or actual terrorist. The current techniques seem to be working well. An aircraft has not been sabotaged or blown up in a long time. I say maintain vigilance with what we already have and don't spend money on unproven new devices. A canine nose is the best detector we have.

A man had just settled into his window seat on the plane when another man sat down in the aisle seat and put his Black Labrador in the middle seat between them.
The first man looked quizzically at the dog, and then asked why the dog was allowed on the plane.
The second man explained that he was from the Drug Enforcement Agency and that the dog was a 'sniffing dog'.
'His name is Sniffer and he's the best there is. I'll show you once we get airborne, when I put him to work.'
The plane took off, and once it has leveled out, the policeman said, 'Watch this.'
He told Sniffer to 'search'.
Sniffer jumped down, walked along the aisle, and finally sat very purposefully next to a woman for several seconds.
Sniffer then returned to his seat and put one paw on the policeman's arm.
The policeman said, 'Good boy', and he turned to the man and said, 'That woman is in possession of marijuana. I'm making a note of her seat number and the authorities will apprehend her when we land.
'Gee, that's pretty good,' replied the first man.
Once again, the policeman sent Sniffer to search the aisles.
The Lab sniffed about, sat down beside a man for a few seconds, returned to its seat, and this time he placed two paws on the agent's arm.
The policeman said, 'Two paws mean that man is carrying cocaine, so again, I'm making a note of his seat number for the police.'
'I like it!' said his seat mate.
The policeman then told Sniffer to 'search' again.
Sniffer walked up and down the aisles for a little while, sat down for a moment, and then came racing back to the agent, jumped into the middle seat, and proceeded to crap all over the seat.
The first man was really disgusted by this behavior and couldn't figure out why a well-trained dog would behave like that. So he asked the policeman, 'What's going on?'
The Policeman nervously replied, 'He just found a bomb.'

Yes dogs are best, but they get bored or tired. Sniffers are getting better, and in fact detect more volatile chemicals than could ever be detected using X-rays, which are limited pretty much to nitrogen-based IEDs or tagged commercial explosives (apparently marzipan has the same signature as Semtex!). X-rays are only really good at looking inside peoples luggage. They can be programmed to automatically identify shapes, certain materials etc. but they are still dependent on human operators (who should be changed every 15mins) to identify threats. Sniffers are generally only good for atmospherically clean environments (e.g. indoors) and where dust is not an issue, which is rarely what you have when a lot of people are passing through. No security check will ever defeat a determined intelligent threat, or a completely random accident, but we do our best. The best security is actually to have a system which filters the threat identification from the moment a ticket is bought, which requires you to know, absolutely, who that person is, and their entire personal history (and probably what they are thinking!) before the ticket is issued. The question is: do you want to live in that world?