I stumpled across this intersting post on RTL-SDR.COM talking about monitoring TirePressureMeasurementSystems with a cheap SDR stick and a clever piece of software. The rtl_433 software receives and decodes signals transmitted by tire pressure sensors inside the wheels of modern (I assume at least from the last 10 years) cars.
My initial idea is, that I can monitor the traffic in front of my house - at least traffic of modern cars. As Germany is a car centric country, I expect to catch most of the traffic.