Make sure the adjustment knobs for sensitivity and on-time for the motion sensor are facing up so you can modify how sensitive your device is and how long it stays on to signal your Arduino.

Using motion detectors and an Arduino you can trigger lights, fans, or even an pneumatically controlled cleaver-wielding clown to help add your house to the “if you dare” list.

If you've always wanted to try to build an Arduino project, this may be a great way to start. Matt Williamson built a tiny, Arduino-based motion sensor that will SMS you when something moves by ...