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: https://www.instructables.com/id/Security-with-a-old-Pentium-1-Part-II/
Also check out: https://www.instructables.com/id/Computerized-video-security-setup/

LIZZYSAF.BAS
Download

Step 1: What's Needed.

Parts:
An old computer with a joystick port, 3 1/2 inch floppy drive, and a network card. (Cdrom and hard drive not required)
UPS
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
Solder
Staples
momentary push button switch for disarming.

Tools :
Soldering iron
Staple gun
MSdos disk with a basic interpreter (i.e. qbasic).

LIZZYSAF.BAS
Download

Step 2: Documentation

Attachments:
Traditional joystick pinout.
The base code for the project written in basic. (you may have to change the code depending on the dialect.

LIZZYSAF.BAS
Download

Step 3: Wiring

It is probably a good idea to just do a temp setup to make sure things are working before a real installation.

Attach magnetic alarm contact switch to a door per it's instructions.
Cut two wires long enough to go from the computer to the
Solder one wire end to pin 2 of the joystick port connector and the other end to one side of the magnetic alarm contact switch
Solder another wire to pin 4 of the joystick port connector and the other end to the other side of the magnetic alarm contact switch
Solder the momentary switch to pins 10 and 12 separately to each side of the switch.
Use staples to attach the wire to the wall between the door and the computer.
Plug the joystick connector into the joystick port.
Plug the computer into the UPS and the UPS into the wall.

LIZZYSAF.BAS
Download

Step 4: Getting the Code Into the System.

I do not intend this instructable to be a tutorial on basic or dos. Please get addition help for a computer technician if you need it. Of course, you can ask me questions via comments also.
You will want to make a dos bootable 3 1/4 inch dos disk. See your system manual on how to do this.
Copy lizzysasaf.bas, qbasic.exe, and edit.com to the floppy.
You will used edit to create or modify autoexec.bat so that the following is the last line.
qbaisc lizzysaf.bas
This will autorun the program when you start the system.

LIZZYSAF.BAS
Download

Step 5: Testing

Connect the phone line to the wall. Turn on the ups and then the computer and monitor. Once you see the program is running, open and close the door several times to see how it works. Information should be written to disk and there should be notification on the screen and a tune should be played if there is a speaker attached to the motherboard.

Note:
In the code PRINT #2, "ATDT1234567;", change 1234567 to the number your want called. If you do not want the modem feature, just do not connect the phone line to the wall. Now I have the system send me an email message from the computer network but that is a lot more involved than I want to get into here.

Step 6: Done.

You can use the disarming button to stop the program if you need to. If that all worked, you are ready to use your system. You can always use edit to look at the disk to see when the door or window was opened or closed. I would back up the files to another system and erase old data-files as the disk becomes full.