Currently, I'm doing this project on smart alarms. The system totally finds but there is one thing that concerns me on how to integrate this system into the home alarm system. I do connect the relay to the pin D (Common) and Z (Zone) on the alarm box, but there is no integration between these 2 systems.
My alarm system process is when the sensors detect above a threshold of gas and temperature, it will trigger the in-system buzzer. Then, a relay will be triggered to integrate the home alarms siren. Seek your guys expertise in this thing to clear me up on this matter.
Your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with (nor for advice on) your project See About the IDE 1.x category.
If that's not sufficient integration, please describe what integration means.
How does alarm box know to look in zone Z? Is there a jumper wire to be removed?
Usually security systems use a loop with constant current.
If the loop is broken, the alarm is triggered.
In that case you would need to insert a relay in that loop and trigger that relay with your homemade stuff.
So instead of normally open most things will be set up as normally closed.
This will trigger the alarm if your device loses power and prevents undetected failure of your security system.
It can trigger false alarms, that might be expensive if you have a security service responding to your alarm...
Basically you (and we) will need info on your alarm system. Let us start with installation guide...
I just make my project relay the same as the magnetic sensor that only has 2 wires instead of 4. The relay uses an open loop. When the system detected fire, then the relay will go closed loop. There is no default on the home alarm system. But, there is no integration from my system with the home alarm siren. Only buzzer on my system are sound but not the home siren.
When the door is closed the magnetic sensor is SHORT so start with a jumper wire from GND to zone Z (what ever that is) and do a simple test to see if your panel is responding to that zone when the jumper is removed.
The more advanced alarm panels use a END OF LOOP resistor that pulls the zone input up to a certain voltage then a short or open on that loop will trigger the alarm.
Can you draw a schematic of the connections from your device to home system?
And add a installation guide for your system as well.
Just google:
'Brand name typeNr installation guide .pdf'
And see what you get.
Or turn upside down that drawer with all that paper stuff that also holds last year's Christmas cards and see if it is there...
Does your relay actually do anything?
In your schematic the ground connection is missing.
Also you should not feed a relay from arduino... (the scheme does not tell how relay is fed unless it is fed from digital ouput pin, but that is not good).
What type of relay module do you have?
Doesn't the alarm system have a brand?
Is it custom made?
Can you make a picture (frontside backside inside).
Type nrs are usually near brand name and/or at bottom/back).
For my relay, yes I did connect the pin as per your statement above. One to GND, one to 5V, and one to Digital pin. On the diagram only I did a mistake but on actual hardware it is correct.
Just as a simple test, can you see a way of integrating a normal push button switch with your alarm system so it triggers the required action when pressed ?
If you can do that, then surely it would be simple to do the same with a relay. However, if you can't even get that far, then the problem to solve is the configuration of the alarm system.
See 
