> "set off explosive detectors. Repeatedly."

If I walk back and forth through a metal detector with a belt buckle multiple times, do I become increasingly suspicious each time it beeps?

It's nothing at all like going through a metal detector with your belt on. Metal detectors check your present state, trace analysis checks your PAST state.

False positives are possible, I've had it happen to me. When "the machine beeped", I got a thorough pat-down and re-swabbed, and the next time "the machine did not beep" and I was on my way.

It's my understanding that TSA agents will not allow someone to pass who is consistently setting off the explosives alarm. What would be the purpose of checking for trace explosives residue if the agents simply disregard it when it triggers?

Of all the 'sigint' they collect on each passenger, I would bet a "repeated trace analysis fail" ranks up there with carrying box cutters as one of the more alarming indicators an agent has to deal with.

It sounds like the agents did everything they could to try to get a green light from trace analysis. Failing that, the passenger is obviously red flagged and it's "all systems go" to determine if they are really a threat. I can't imagine how else they would handle it.

Passing a belt buckle through a metal detector repeatedly and passing a sample through an explosives detector repeatedly demonstrates nothing except that the alarm was not transient.

Just because it isn't transient doesn't mean it isn't a false positive as this story demonstrates.

With such an overwhelmingly massive chance that the alert was a false positive, the response the author received is indefensible.

They were specifically highlighting the pointless use of the word "repeatedly" for emphasis, I believe. Well of course it happened "repeatedly"; they just repeated the same test with the same articles.

At the very least it confirms suspicions that you do in fact have metal on you. By removing doubt, you do increase suspicion.

It doesn't confirm that the machine results were not a false positive, it only provides you with some assurance that the results were not transient: https://news.ycombinator.com/item?id=6260688

So....in other words you are provided with more assurance of your suspicions. Thus increased suspicion.

Though you may call them explosive detectors, they aren't. They're chemical detectors, specifically mass spectrometers. All they can do is detect chemicals, and they obviously can't tell the difference between some common chemicals and a true explosive device.