Instead of complicated stuff, what about the ol' citizen's band radio or CB? Everybody has one of those. I have three. Good for local anyway. And 12 volt. Very inexpensive.
Offered by Clip.
I think it would be a very good thing to have. Although they only pick up stuff at relatively close range, any roving groups will surely be using scavenged radio equipment. CB and police equipment would be the most commonly used by such groups I would expect.
Offered by Ron.
WB5KAN - General Class