Maybe "Tabitha" will post here about the pros of the Pod Tracker that can tell you exactly where your cat is anywhere in the world! Your cat would have to wear a collar for it to attach to. But, Tabitha swears by the product and both of her cats wear them. Her cats go out during the day but are inside at night (and she's charging the batteries -- you get an extra with it). You can track your kitty's adventure as well. I have one for the outdoor cat, but he refuses to wear a collar. I've tried three on him, including an elastic one, and he shows back up with it gone!
I love our pod trackers but wouldn't view them as an anti-theft device which is one of your concerns, purely as I'm sure if someone stole a cat the first thing they'd do is remove the collar.
However for piece of mind about the whereabouts of your cat they're great as you will know where to find it or if it's managed to get into a vehicle and end up miles from home. Which happened to us and why we now use them. Our two were already used to collars so it was no big deal adding the pod, they're only 29g in weight and the size of a cork.