ArPI is Raspberry PI Zero W based home security system which I started to build 6 years ago in 2016. The base idea was to improve my actual home security system. The major issues I had with my original security system:

Programming: almost impossible to make any changes in the settings through the keypad. For a simple access code change you need to spend a lot of time to learn the key combinations.
Feedback: to find out what the reason of an error, to see the alert history...or getting any information from the system was horrible.
Remote: for accessing the security system remotely I should buy another expensive component for the system.
Causeless alerts: usually when we went to vacation for a week our neighbors called because of the sirening home.

I didn't want to buy a new smart home security system for a lot of money. I wanted to build it for a lot of money 😃. So, I decided to replace the main board of the old home security system with my solution and keep the already used sensors, siren. For that I chose a Rasperry PI Zero W and designed a PCB which can interface between the Rapsberry PI and the original components.

As a good starting open you can open https://www.arpi-security.info

In this Instructables project I would like to explain how I replaced my main board to ArPI.

Supplies

Used components:

Raspberry PI Zero W: https://thepihut.com/products/raspberry-pi-zero-w
ArPI Rasberry PI hat: https://www.arpi-security.info/
UPS: https://aliexpi.com/q9br
Wiegand keypad with card reader: https://aliexpi.com/QrSs
RTC DS3231: https://aliexpi.com/ZNU8
2G GSM module: https://aliexpi.com/zjQi

Step 1: Preparation: Remove Old Main Board

As preparing for replacing the old main board I took some photos of the old security system cabling and noted the colors and connections.

Finally I removed the old main board 😃

Step 2: Connecting Basics

First I connected the UPS and the ArPI board on terminals 12V and GND. Also connected the cable from the UPS to SE to identify power outages.

After that I connected all the sensors of the system to the terminal CH[1..7] and GND.

The siren is connected to 12V and the GO-/GND on the board.

For the setup of the software please read: https://docs.arpi-security.info/en/latest/developers/installation/

That's the minimum setup and I tested it for a week.

Step 3: Connecting GSM and Keypad

Removed the old keypad and connected the new Wiegand keypad to the terminals BL, RE, D0, D1, D2.

Connected the GSM module to the GSM pins. TX to RX and RX to TX! Also added an external antenna.

I tested the upgrade and did some fixes in the code 🙃

Step 4: Conclusion

The system works now and I'm testing the stability, although it was running on my desk in a test setup for more than a year. I did a tutorial for the family and waiting for their experience and feedback.

Currently I can't close the metal box of the main board because it block the WiFi connection. So, I will need an external antenna for the Raspberry PI Zero W as, well.

Future ideas:

Improve code quality with testing. I had no time to automate testing...
Adding features:
Silent alert: no siren, only sending notifications
Multiple emails and phone numbers
Improved hone screen with sensor states
Improved history: storing sensor states when not armed
New notifications: power outage
Improving the board:
Check battery health
Better PCB layout: all the terminals on the same side. Use with other Raspberry PI variants.

Step 5: Upgrade

A new version of the board was created in 2023 and replaced the old.