Directional input devices

Function
A directional input device is a class of contraption that tests whether the player is facing in a certain direction, and trigger an input if that is true. These contraptions are usually used in "don't look back" style stages.

Building
Directional input devices make use of the fact that boos only move forward when Mario is not facing them. The boo has a muncher stacked on it, and when the boo moves, the muncher will move forward. This will cause the bob-omb to explode, triggering a P-Switch or POW block contraption segment.

Simple directional input device
A simple directional input device is a contraption that triggers a POW block, P-Switch, key, or other contraption if the player looks in a certain direction. It can be used to make a levels where mario must look forward, or his path will be blocked.

Complex directional input device
A complex directional input device is a larger directional input device that prevents the boo from roaming around after the device is triggered. This is because of the clown car which bounces off of the springs, and carries the boo. This contraption can be hooked up to any input. A link to this contraption in use can be found here.

Extra tricks
Any directional input device can have 2 inputs if it is mirrored.