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/
Step 1: What's needed.
An old computer with a joystick port, 3 1/2 inch floppy drive, and a network card. (Cdrom and hard drive not required)
Nearby wall phone plug
Modem (to have th system dial your cellphone or where ever)
Several magnetic alarm contacts. (nc - normally closed)
Lots of almost invisible wire.
DB15 male joystick connector
A shield for same
momentary push button switch for disarming.
MSdos disk with a basic interpreter (i.e. qbasic).