Action_owl (awes name!) set up a versatile intrusion detection system using Arduino + Processing -
This instructable will show you how to construct a laser tripwire that can twitter and grab an image from a webcam, as well as execute any command you can put in a bash script. ThisÂ instructableÂ is actually quite simple and is even suitable as a beginner arduino project. It requires a GNU/linux (or possibly Mac) operating system with the arduino IDE and Processing IDE working properly.
Sounds like a good way to keep an eye on your pad while out and about – check out the full project deets here.