Garmin has just introduced the Chirp. It is a small transmitter that can send details to compatible handhelds. You can send hints, coordinates, all kinds of things. The unit is very small making it easy to hide almost anywhere. I was out with the BFL crew last night and Avernar had the chirp with him. We were seeing able to activate with as much as 10m between devices.
I imagine this could take Whereigo or proximity games to a whole new level. Multi-caches could take on a new dimension also. Maybe cachers will hide bonus caches that you can only find if you have the chirp. Would that be a good thing?
The technology is very new consequently only the latest GPSr will support it. My Colorado has the underlying technology but the unit’s firmware does not support it. I can see a lot of upgrades coming if people can find imaginative uses for the Chirp.