About 8 years ago I played golf while on vacation, needless to say I got pulled aside because my shoes had "nitrates" on them. As any good golf course uses fertilizers.
Lessened learned for me...
The idea is, if you are dumb enough to try and work or implant these devices/ chemicals, you will most likely have some sort of residue on you. I'm not sure how long these chemicals stay on you or the tolerance of the machine, but a few parts per million might be enough to catch you.