From
http://www.vitalalert.com, the current front page:
THE WORLD'S FIRST THROUGH THE EARTH WIRELESS EMERGENCY COMMUNICATIONS NETWORK
[...]the first and only fail-safe, pre and post disaster, digital, wireless, early warning, emergency and evacuation network, capable of sending 2-way voice and text communications through earth, skyscrapers, subways, tunnels, ocean and more. EBN can be used in urban, subterranean and ocean environments.
This technology is not 'radio' and does not have the short falls of radio, which is line of sight technology. EBN technology has the ability to penetrate the earth by sending vital information through the earth for several miles or through steel and concrete buildings. Rock, concrete, steel, debris and dust cannot stop the EBN communications signal. It is the 'real' solution to radio failures that plagued warning and rescue operations during disaster and extreme environmental situations[...]
From
http://www.ddj.com/blog/portal/archives ... d_rad.html (source: Dr. Dobb's Update, August, 2006, Issue 1,
http://www.webreview.com/maillists/):
Underground radio uses very low frequency (VLF) electromagnetic radiation and digital audio compression technology to carry voice and text data. The VLF signals also can transmit tracking and location data for radio users in the case that they are unable to respond.
"This is a technical solution to the problem of voice communication in underground areas. It is also inexpensive to build," said David Reagor, the principal investigator of the Los Alamos [National Lab] team who originally developed the technology.