http://www.cellular-news.com/story/18558.php
"Cellular phones have become the latest epidemic in prison contraband, posing a danger that extends beyond prison walls. Correctional authorities have indicated that cellular phones have become more valuable inside a prison than drugs or other contraband, and are often referred to as the new prison cash because inmates can sell minutes or cellular phone use to other inmates.
The GEO Group, the second largest private prison management company in the USA, says that it is now implementing a new application of patented high-tech equipment for detecting and locating hidden contraband cellular phones (even if the phone is not transmitting or even turned off)."
