You can easily get actual "DO NOT FEED" cat collars, which may be a slightly better option.
The tracker Nicci shows, is actually design for geotagging photographs. The idea is that you synchronise you camera's time to GPS (ie UTC) time, and then the software can add the Lat Lot to the EXIM data on the images.
As I recall, it uses Windows software to download the GPX data, but I believe someone was working on Linux software to do the same, so slightly simpler and less clunky software may be available, if all you want to do is dump a GPX file onto your PC.
There's an active tracker available now, which has GSM and WiFi, so you can track the cat whilst it is out wandering around, and more importantly, if the collar goes AWOL (because of the safety release, to stop the cat throttling itself), you can probably recover it!
PawTrackIt looks to be a bit bulkier than traditional cat collars, but it is a lot smaller than similar devices built for dogs.
If Kai still visited the house, I'd get one for him, but Zev is much more the homebody, and doesn't ever seem to go far from the house, so the expenditure would be wasted on her. Male cats do tend to wander a
lot further than females, theoretically in search of mates, although that's no longer a problem with Kai, since he was "done" shortly after I acquired him.