This laser tripwire project allows you to twittering and grab an image from a webcam or execute any command in a bash script when someone crossing the tripwire. The project construction is simple, you just need to position Laser pointer and LDR in a fixed position, then bounce the laser to the LDR with a mirror. When something block the laser, the LDR will give signal to Arduino to take action, grabing image and tweetering status. You may need to adjust the threshold values depending on your LDR.
This security project requires a GNU/Linux (or possibly Mac) operating system with the arduino IDE and Processing IDE. If you created a more complex processing application. To implemented in Windows you need create complex processing application for it.
Watch Laser Tripwire In Action:
Project Documentation and Source