AUX button on key fob for 08 Ford Focus SES?

Just got the car, and I'm not sure what it does. I also know there's a wire coming from my rearview mirror that looks like it is for an antenna or even an alarm perhaps? Any ideas?

An aux button is generally for "other" features… It can be programmed for an alarm, yes

Are you not able to read the car manual? Nothing should be exposed on the rear view mirror. I suggest that you take the car to a mechanic as to that wire. Reading the car manual should be the first thing new car owners MUST BE asked to do, not to reach for the smartphone.