"Blu Eye" monitors radio traffic activity used by emergency vehicles and alerts when they are in close proximity. It does not allow someone to actually listen in on radio transmissions, but alerts to the presence of an emergency vehicle (police, fire, ambulance,etc.) up to 1km away. Made by Target Automotive, the device can detect pulses sent over these channels every few seconds, so it works even when there are no transmissions. $1,600 and only available in the UK for now, but a model for the USA's P25 protocol is on the way.
I like the idea if they cut the price to about $400. And only if they allow a Bluetooth connection to a smart-phone, WITH an ap that runs in the background and notifies with a pop up window.