Software-defined radio (SDR) is a radio communication system where parts of the components are implemented in software. Cheap USB digital TV-receivers usually work this way, and specific chipsets can even be tuned to a frequency of your choice. And that's where the fun starts: with the right software, not only digital TV but all sorts of radio communication can be received... This session will explain the basic concepts of SDR and show how to use a 7 dollar USB stick to receive and decode maritime AIS messages from ships and ADS-B messages from transponders of commercial airliners. I will demonstrate how to process and visualize the data, resulting in a web application that shows the actual state of ships and airplanes around the location of the receiver.