Human traffickers implant people with RFID chips
This is weird, and scary, but also sorta dumb? Since RFID can't be used to locate someone, my best guess is that this was done as a form of psychological manipulation- tell a person you are implanting a tracking chip, implant any damn thing, they believe they are being tracked. That, or the asshole doing the implanting actually had no idea himself how such things work. Effectiveness, aside, this remains unspeakably evil.