Here’s an interesting gadget that will respond to how far you are away from the computer and also twitt your distance. I am not exactly sure what the point of this is but I am sure it can easily be applied to system security and related things.
arduino & sonar returns your distance away from the computer and it is displayed on the screen. the farther away you are from the computer the larger the text and the greener the screen. the closer you are, the smaller the text and the redder the screen. get within 5 inches and a buzzer alarms. distance is twittered.