Ok, I had to go and check what an "Ion Tracker" is. Turns out it's a mass spectrometer. I assume it's the same device they use at airports for checking for explosives, when they swab your bag and then stick in a machine.
Seems they might be a little too sensitive according to this article, where a welsh assembly member asked for a demo and tested positive to canabis himself, as did another assembly member.
"You could pick it up from anywhere couldn't you?" she said.
So does that mean when they do the swab thing in the airport they'll know that I've been touching weed the night before? Or they just ignore that spike on the graph and only stop me if the semtex one is high?