The set-up process is very simple, and best understood by referring the wiring diagram. If everything goes right,you should see the burning eye of the red LED when there is no object in the safe-zone ...

Buy arduino, buy sound shield, buy distance sensor shield, plug into each other, burn example code, stuff components inside box. Not only is this not a hack but he might as well have just bought a ...

One way to accomplish this involves four HC-SR04 ultrasonic sensor units that transmit data through an Arduino into a Linux computer. The end result is a virtual touchscreen that can be made at home.