I sat next to a pyrotechnician on a flight to MacKay once. I asked him if he ever had trouble with a security check, having handled explosives. He said never. He'd been tested often. He went on to say, he handled all the nitro and sulphur compounds that are supposed to show up on those wands, and should be all over his jumper.
So what use is it..!? Do you have to literally have an explosive vest strapped on to get a positive?