Hi everyone, I’m really excited to share my recent project with you! I’ve been working on integrating my smart door sensors with my existing home alarm system, and I wanted to walk you through the process and share some tips along the way. 
So, here’s the backstory: After having a conservatory fitted, I realized I needed a way to monitor the new door without running additional cables or disrupting my home’s decor. I initially looked into adding a commercial wireless door sensor to my existing alarm system, but I heard they weren’t very reliable and were hard to find in the UK. Then, I thought about using a Z-Wave door sensor and integrating my alarm into SmartThings. It seemed like a solid plan, but I had a few ground rules:
- Reliability: I didn’t want to rely solely on SmartThings for my home’s security. It’s just not reliable enough for that.
- Offline Functionality: If my internet goes out (which is unlikely, but still), my alarm should still work, except for the conservatory door.
- Control: The existing alarm’s keypad should remain the primary method for arming and disarming.
- False Alarms: I really didn’t want to deal with false alarms—my wife would be less than thrilled!
- Power Outage Backup: My existing alarm has a 12V DC battery backup, so I wanted to make sure the Z-Wave integration could run off that if needed.
Phase 1: Getting the Alarm to Communicate with SmartThings
My first goal was to have my alarm notify SmartThings when it was triggered. I decided to use a Fibaro Door Sensor, but after some research, I found that using a ‘wet’ sensor (which is cheaper in the UK) with a relay could work. The idea was to connect this to the 12V supply from the alarm panel. When the alarm goes off, the siren is powered, which in turn activates the relay, notifying SmartThings. I even included a small voltage regulator to power the sensor directly from the alarm panel. Here’s a quick breakdown of how it worked:
- Siren Activation: The siren’s 12V supply triggers a relay.
- Relay to SmartThings: The relay then activates a water sensor, which sends a notification to SmartThings.
Phase 2: SmartThings Activating the Alarm
For this part, I wanted SmartThings to be able to trigger the alarm. Most wired alarms use a continuous loop per zone, so I decided to use a separate zone loop and a Z-Wave relay to break the loop. I used an Aeon Z-Wave relay (which I had lying around) and an additional 240V relay to break the loop. Everything was neatly mounted in a small project box for safety and neatness.
Testing and Results
During testing, the alarm responded to the Z-Wave relay instantly, and the water sensor notified SmartThings almost immediately. I even wrote a quick smartapp to handle notifications and tweak some Device Handlers to make everything look good in SmartThings. It was a lot of trial and error, but it paid off!
Lessons Learned
- Plan Ahead: Make sure you have all the necessary components before starting. I almost ran out of relays halfway through!
- Safety First: Always double-check your wiring, especially when dealing with 240V. Safety should never be compromised.
- Documentation: Keep detailed notes of your setup. It makes troubleshooting much easier later on.
Final Thoughts
This project was a great learning experience, and I’m thrilled with how everything came together. It’s amazing how much you can do with a bit of creativity and some off-the-shelf components. If you’re considering something similar, I highly recommend starting small and gradually scaling up. And remember, don’t be afraid to ask for help—this community is full of amazing people who are more than happy to assist! 
If anyone has questions or suggestions, feel free to drop them below. I’d love to hear how others have approached similar projects! 