"A British man sentenced to four years in jail in Dubai after cannabis weighing less than a grain of sugar was found embedded in the tread of his shoe has reportedly been pardoned ... The 43-year-old was arrested in September  at Dubai International Airport ... Customs officers found 0.003 grams (0.0001 ounces) of cannabis in a cigarette stub stuck on the sole of one his shoes."
-- Sky News
When I read that I wondered how on earth Dubai customs found the traveller's "stash." I mean, just think about it; thousands of people passing through customs every day and the officials can spot something that tiny on the sole of his shoe! There has to be some kind of logical explanation.
Before I go any further, I must explain that the United Arab Emirates (the UAE), while considered perhaps the most liberal of the Arab Gulf states, is fanatically (and irrationally) anti-drug to the point where entering the country with melatonin tablets (an over-the-counter medication used to counter jet lag) or traces in your bloodstream of a whole list of chemicals will get you arrested!
Want crazier? It was reported in 2008 that a Swiss national went to jail for four years in the UAE when customs found -- and I'm not kidding -- three poppy seeds on his clothes from a bread roll he consumed at Heathrow.
Now, you're probably wondering how on earth could UAE customs detect 0.0001 ounces of cannabis or three poppy seeds? A 2008 BBC report quoted Fair Trials International's chief executive, Catherine Wolthuizen, who claimed that "authorities were using highly sensitive new equipment to conduct thorough searches on travelers."
I can't find any reports of exactly what kind of "highly sensitive" equipment was in use in the UAE in 2008, but I can tell you that by 2010 UAE customs was using full body scanners.
There are two types of full body scanners: Backscatter X-ray scanners and millimeter wave scanners.
Backscatter X-ray scanners "bounce" X-rays off people and questions about the safety of these devices still remain unanswered (you can buy [radiation shielding underwear][http://www.rockyflatsgear.com/] if you're worried or shy).
Millimeter wave scanners (which are, apparently considered safe) operate in the sub-terahertz band (non-ionizing radiation with a wavelength greater than one millimeter) and are either passive (which detect natural millimeter radiation) or active (which "bathes" the target in generated millimeter radiation).
How good are these systems? Apparently not very good as both types of scanner have a limited ability to "see" through multiple layers of clothing and can't examine body cavities.
According to a Wired article from 2011: "A study published in the November edition of the Journal of Transportation Security suggested terrorists might fool the Rapiscan machines and others like it employing the X-ray "backscatter" technique. A terrorist, the report found, could tape a thin film of explosives of about 15-20 centimeters in diameter to the stomach and walk through the machine undetected."
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