Here's the thing: If I had a Bluetooth GPS and some programming chops, I could make a Colorado Detector. It just takes 4 coordinates, and if you're inside them, Colorado, if not, not. I think this would be enormously funny. One could also program it for Wyoming and Utah. You can even get chipsets and do some device hacking, and then have an indicator light or small display in a handheld unit.
A project for the future.