Probably coded to their DNA or something, seems to be beep more as a person gets closer to the target, so it has to be tied somehow to that person in some manner and if it was an implant ppl would just remove it. So possibly tied to the person biologically ?
Yeah, this makes the most sense. I could definitely see a blood draw being required by powerful figures making risky deals as an insurance measure. The only hiccup that I can see would be that it creates a situation where one would have had to already accessed the DNA of the target. In a case like The Child, it then calls into question how they got that DNA in the first place but lost the child. So I doubt they ever really explain the tech because it would require explaining more backstory detail that doesn't really serve the forward momentum of the story itself.
The type of storytelling this show operates on relies heavily on minimalism. It creates the tension, enhances the drama, and maintains the mystery that helps keep the audience returning episode after episode to get that next little bit of a reveal. It also makes it harder for the most critical minded audience members to pick it apart using minor detail conflicts.
