I like the idea of a passive rfid tag on each piece, and readers on every door to track movement.
The passive RFID tag will just sit there and not emit anything unless you are walkint thru the door. That is good if you are doing RF testing in the lab, as you do not want active transmitters going off all the time when you are making sensitive measurements! Man, I get spurious readings in the lab all the time now, and it is virtually impossible to shut everything down to find the source. You do not want your test equipment RFID tags adding to the problem.
Not knowing much about RFID tags, am not sure how well they work when glued directly to a metal surface. Maybe need one with a plastic package that stands the chip a little off the metal surface.