Sixteen-year-old Alexander Kendrick has put together a low-frequency radio which allows for the transmission of text messages from caves nearly 1000 feet (300m) underground. I still can't get a single bar of reception on the subway.
Aside from updating Twitter with messages of "It's dark in here" while spelunking, Kendrick's science fair-winning cave-texting device could actually help save lives. Underground rescues in caves or mines are time consuming and dangerous ventures because of the rescue teams' inability to communicate well - unless they lay down miles of telephone line as a rescue team in new Mexico once did. With this cave-texting system, rescuers would be able to maintain contact and potentially get medical aid where it's needed a heck of a lot faster.
Of course Kedrick's project isn't the first cave radio, but its test was actually "the deepes known underground digital communication ever to take place in the United States.". I hope the text was "Hello World." [NPR via Slashdot via Make]