Sniffer machines etc.
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?
