Car Whisperer: The Car Whisperer is a proof of concept tool to eavesdrop on conversations in other cars when the speaker is using a Bluetooth handset.
The carwhisperer project intends to sensibilise manufacturers of carkits and other Bluetooth appliances without display and keyboard for the possible security threat evolving from the use of standard passkeys.
Found via this IHT article, which expands on it:
Using a laptop computer with a Bluetooth transmitter and software that runs on the Linux operating system, the Car Whisperer has a range of 300 feet, or 90 meters, about 10 times that of Bluetooth hands-free systems. The range can be considerably extended by adding a directional antenna.
I bet some law enforcement agency somewhere is already exploiting the crap out of this.