My car uses multiple resistors in a 'ladder' and shorts them out according to which button is pressed. I get a different resistance along the wire for each button that is pushed. To answer your question: Yes, its a single wire which transmits a variable level of resistance.
It is not a digital signal, although that would be fun to interface with
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I've just given someone a beta copy of my app to test. I'll let you know what happens shortly.