Automatic Packet Reporting System — APRS — is rather clever. It’s a way of reporting position, status or messages via the amateur radio 2m band. Data is relayed via digipeaters, and routed to/from the internet APRS-IS system to any user worldwide.
It’s a little fiddly to set up, even with a very polished (read: $$) handheld radio like the Kenwood TH-D72A. I’m a bit disappointed that the purported SiRFstar III GPS in this radio takes forever to get a lock, but it’s a nice radio despite this.