I bought it at my LHS for 21$.The LED blinks red the whole time the truck is on and turns solid red when it lose's signal.I'm not sure if it changes colors with a low battery or not because it's under the radio tray and I can't see it lol.It only came with instructions on how to hook it up and set it so I guess thats all it does.It works good.Tower doesn't seem to stock it but you could try
www.nitrohouse.com they stock alot of Ofna stuff and they might have it.