It seems technically interesting but societally problematic. For example it appears to greatly simplify stalking and harassment. How can a domestic violence victim avoid their attacker if their movements are so easily monitored? Perhaps use this to identify people walking away from a gay bar or a political meeting to set up a bashing? Note when somebody leaves home in order to rob their place? And bear in mind that for some individuals the cost of being identified back won't outweigh the value in being able to locate their victim.