51

Before entering a commercial plane, I had to go through the usual security check at Prague airport (PRG). When I passed the metal detector, it went off. I assume it was because I forgot to take off my wedding ring.

I was approached by the security guy and instead of a full check (which I was expecting), the security guy marked both sides of my hands with some piece of wet paper, told me "wait there", left with that paper (maybe checking something with the paper, I do not know exactly) and after some time he told me I was free to proceed to the Duty Free zone behind the security check.

While relieved, I am wondering: Does anyone have a clue what kind of security check was that?

JoErNanO
  • 52,873
  • 18
  • 166
  • 277
Pavel Janicek
  • 573
  • 1
  • 4
  • 9

4 Answers4

50

Often at security they swab my backpack and some of my possessions with a small piece of damp paper. It is supposed to pick up traces of the materials I've been handling. Then they put it in a machine that analyzes those traces. At customs and immigration it's set to detect various illicit drugs (I've seen this on Border Security) but at security I believe it's set to detect explosives.

Certain people are chosen randomly for a swab. Since you had no residue on your hands that would require them to inspect you further, they sent you on your way. This wasn't caused by you leaving a ring on. Leaving a wedding ring on is fine.

Kate Gregory
  • 82,075
  • 14
  • 237
  • 340
19

The swabs are used to check for explosives and/or drugs. Indeed, if you manipulated any such substances in the near past, it's likely that traces can still be found on your hands, and on the things your hands usually touch: bag handles, zippers, pockets, etc. If you pay close attention during the checks, these parts of your personal belongings are the ones that are usually swabbed. The TSA blog calls these swabs state of the art Explosives Trace Detection (ETD) tests:

While going through checkpoints, you might have seen officers using little white swabs at TSA checkpoints at one point or another. In case you had no idea what our officers were doing, they were conducting state of the art Explosives Trace Detection (ETD) tests. And all along you thought they were giving your items a complimentary cleaning…

ETD tests are used in checkpoint, checked baggage, and cargo environments. We swab things such as laptops, shoes, film, cell phones, bags, wheelchairs, hands, casts - you name it. Certain procedures call for an ETD test.

Basically, our officers run the white swab over the area in question to collect a trace sample. They then place the swab in the ETD machinery which analyzes the sample for extremely small traces of explosives. The test takes a matter of seconds.

[...]

So as you travel, you might be asked for a swab of your hands at the checkpoint or gate. It’s painless and quick. The swabs are disposed of after each use and will not be used on more than one person.

Community
  • 1
JoErNanO
  • 52,873
  • 18
  • 166
  • 277
7

This is a way to check if you have manipulated explosives recently. The paper will absorb the particles and then react during their test afterwards.

Olielo
  • 6,168
  • 4
  • 24
  • 37
5

Something that hasn't been noted by others is that while this is testing for explosives, it can also pick up residue from firearms usage e.g. if you've been shooting and/or handling ammunition, particularly spent casings like shotgun shells it can also cause these tests to come out positive.

If you have been shooting say at a range or you've been clay-pigeon shooting etc. it could be a good idea to take a receipt for that to the airport with you to avoid misunderstandings.

WhatEvil
  • 540
  • 3
  • 6