The laser tripwire project is superb project for both experienced and brand new Arduino enthusiasts. It combines both hardware, software, and communicating between the two. The simple project captures a snapshot of an unauthorized entry and alerts the homeowner via Twitter. The security project is built around an Arduino board, a laser pointer, a photoresistor, and a webcab.
The laser is reflected across a doorway into the photoresistor which is connected to the Arduino When the door is opened, it trips the beam which sends a signal to the Arduino. The Arduino forwards the signal to the computer which then executes a program written in Processing. The software then logs into Twitter as it captures a photo from the webcam and then posts a link to the photo as we ll as the exact time of the break-in. Check out the detailed steps and the source code to setup a dirt simple DIY security system.