Where is that black switch at? Is it a toggle (on and off), or a push button (momentary on)? If it's push button, it may be the valet/programming button.
Do you have a light on the key fob that lights up when you push the button? (Mine is green, and in between the two buttons.)
Do you know where the other components of the alarm are? There should be at least a brain somewhere, and possibly a vibration sensor in addition to the motion sensor.