> Well, there are several reports from HN users in this thread that describe situations in which it could allegedly occur Which makes the detectors useless as

> Well, there are several reports from HN users in this thread that describe situations in which it could allegedly occur Which makes the detectors useless as an interrogation tool. If the alarm sounds, then check the person for explosives. That makes perfect sense, it's a useful tool for finding explosives on people. But if you cannot find explosives on the person, what do you do then? Any even slightly training terrorist is going to know what other products would produce the same detection result as the bomb they just built. So they'll pretend to think for a while, and then say "I work in a supermarket, and a customer dropped hand lotion on the floor this morning, and I had to wipe it up... can that set off your machine?" It seems like there's a magic answer you can give that will let you go free, you just need to know the right thing to say. If the investigator likes you (i.e. thinks you're probably not a terrorist) they'll give you hints about what you should say. If they don't then you're on your own. Someone who can give the right answer is either: * Good at analysis, so they can make a good guess of what might be setting of the machine. * Someone who's been through this before * Someone who got a friendly hint from the investigator * A not-so-dumb terrorist Someone who can't give the answer is either: * A normal person * A dumb terrorist Given the low prevalence of terrorists, that would be the least likely explanation in either scenario, so the whole line of questioning is pretty much useless, except as a way of applying pressure to someone who you've decided is worth applying pressure to. When that decision is based on some genuine piece of evidence, then it might be a legitimate law enforcement technique. When it's based on the gut-feel of the officers in question, it becomes a front for racial profiling.