I originally used an old pc-xt for this project. Doubt you will find one now. Anyway, I decided to put the original software back to work. Not only does the system detect openings and closings of doors and windows, the time date stamps are saved to disk for later inspection. With one joystick port you can have up to 4 entry points. We are only using one entry point with this demo. With advanced programming and electronics, more entry points can be supported. To save electricity, I only use the system when we are gone or when I want to know when my daughter came home last night. Of course the computer needs to be in a secured location. Try this at your own risk. I will not be responsible for any possible shortcomings. Let me know if you have any challenges.
r = STRIG(1) s/b r = STRIG(0) depending on your system.
Update: you should be able to download the code now if you could not already.
Part II: http://www.instructables.com/id/Security-with-a-old-Pentium-1-Part-II/
Also check out: http://www.instructables.com/id/Computerized-video-security-setup/