I like the idea of this app, but it would be great if this app has a car mode in which the UI consists of just two elements: The frequency (on which the transmitter is currently set) and a big button "search". When the button is pressed, the app searches for a free frequency (the frequency with the most "free space" to the next occupied frequencies) and sets the transmitter to this new frequency.

If I'm driving in my car, I don't want to know how many frequencies are free and I don't want to set my own threshold :-)