The last few months have seen an explosion of activity in the field of Software Defined Radio (SDR), after it was discovered that cheap USB TV tuners based on the Realtek RTL2832U chip could be dialed into frequencies well outside their advertised ranges. What was designed and sold as a simple device for watching TV on your computer could be turned into a radio capable of receiving anything between 64 MHz to 1700 MHz with open source software.
Now, anyone with about $20 USD to spare can tune into everything from police and fire transmissions to the International Space Station.