Just use GPS receivers embedded in some items, and watch where they go. You can’t use exploding dye packs, hehehehehe.
This is what you get when you check your bags, and it’s always been that way. When I flew to Australia 30 years I missed my international connection in San Fran, so Qantas “secured” my bags in a pre-clearance area til the next day. When we arrived in Perth one bag was missing; the one full of new Levis ect. from the States for Mom and Dad. (They were living there at that time.) Qantas reimbursed us $60. The contents were worth at least a grand. Never checked a bag since, never will again.
I checked an extra cell phone in my luggage once. I got off in Miami, but my cell phone traveled on to San Juan where it made calls for the next three weeks, according to my phone records.