An interesting (and exciting) article from Wired magazine GNU Radio Opens an Unseen World
about using open source radio software and capturing *all* frequencies…

One of Ettus’ USRPs, with the right daughterboards and radio software, can capture FM, read GPS, decode HDTV, transmit over emergency bands and open garage doors.

…he turns the laptop around to reveal a set of vibrating lines in humps and dips across the screen, like a wildly shaking wireframe mountain range. “Here,” he explains, “I’m grabbing FM.”

“All of it?” I ask.

“All of it,” he says.

Other uses include using GNU Radio to track foot traffic in U.K. shopping centers, by listening for control-channel signals of mobile phones carried by nearby shoppers.