In the microcontroller era today, Arduino ... Infrared (PIR) Sensor. The PIR Sensor detects the motion of a human body by the change in surrounding ambient temperature when a human body passes across, ...

Here is a simple general-purpose security alarm circuit built on the Arduino platform. It brings up an obtrusive alert signal when an intrusion/theft attempt is observed by its front-end sensor ...

Using motion detectors and an Arduino you can trigger lights ... A simple way to think of the sensor is a switch; the diagram below explains the difference between the two approaches.