NewScientist

What are full body scanners?

Remember the X-ray specs of science fiction comics that would let people see through walls and clothing? Full body scanners are a bit like them. The scanners take advantage of the fact that at certain wavelengths, electromagnetic waves can pass through clothes but not through the skin, metal or substances such as drugs and explosives.

If your eyes were sensitive to these wavelengths like the scanners, every person you meet would appear naked, with pens, coins, belt buckles and the like magically festooned about their person. You would also be able to see if they were carrying a knife, gun or explosives.