ID verification will help rule out a lot of casual stalkers but it won't help with the slightly more experienced ones who know how difficult it is to prosecute. "Oh they must have stolen the tracker to frame me!" "I accidentally dropped it in their bag" and similar WILL be a case's undoing in court. If you make people register what the tag is for as part of the verification process, actually have a human check the answer on the other end when they submit their answer that it's specific enough, and periodically make them re-verify this (eg every time they cange the battery, have a pop up "are you still using the tag for xxxxx") means only the most meticulous planner can use it to stalk. At which point the tracker is realistically no more of a vector than the victim's laptop.
You can't convince the police or a judge that you dropped the tag in someone's car if you're supposed to be using it on your cat's collar for example.
Surely then a stalker just needs to be bright enough to make up a story like "I put it into my bag or wallet when I go out, and since I only have one tracker I often move it between them depending on if I have much cash." rather than "I got it for my cat"? That story took under a minute to come up with, I imagine there are even smoother ones a stalker could think of with 20mins effort.
Or at the expense of making it a little bigger, superglue something like a usb stick and you've always got an excuse to have it in your pocket until you "lose" it. Hell, isn't not wanting to lose a coat that you claim to often leave places a good enough reason to have one in your pocket?
You can't convince the police or a judge that you dropped the tag in someone's car if you're supposed to be using it on your cat's collar for example.