Detecting an intruder and setting off an alarm

Let's dive right in to the wonderful world of motion detection!

The basic idea of motion detection is pretty simple from a computer's point of view—the motion detection software processes a continuous stream of images and analyzes the positions of the pixels that make up the image. If a group of contiguous pixels above a certain threshold starts to change from one frame to the next, that must be something moving. The tricky part of motion detection is weeding out false positives triggered by naturally occurring changes in light and weather conditions.

1. We'll be working with a motion detection application called Motion. Install it using the usual command:

   pi@raspberrypi ~ $ sudo apt-get install motion
   

2. With Motion installed, the next step is to create a configuration file for our webcam. The Motion installation puts a sample configuration file inside the /etc/motion directory. We will use this configuration file as a template and modify it for our...