As you can see, the data displays for a set amount of time after motion is detected, and then hides.
This was achieved simply by wiring the PIR module to one of the GPIO pins of the Pi, and then reading the state of the pin in Processing (which now has native support for hardware IO built in to the Raspberry Pi distribution).
The next step is to use an optocoupler to get the backlight of the screen to turn on and off using this same method, to allow the screen to be completely hidden from view when the mirror is idle.
Nice post here. You sure is very techy.