I was researching on a way to get my Vista 15p Alarm Panel to talk to Home Assistant without the Cloud. It can take up to 30 minutes to get a notification because how slow the Total Connect Cloud can be, after all their backbone is IFTTT.
I found a GitHub project called VistaECP that uses a ESP8266 with ESPHome and a few cheap parts that emulates a Keypad set for Address 16. Typically Address 16 is reserved for Programming but it’s totally fine. I can address my 6160 Keypad to 17.
I’m not too fond with the Schematic that is shown on the GitHub Page. The Voltage Divider for the TX. I’ve seen some nasty stuff happen to these Vista Panels when you over charge the backup battery.
This is a revised circuit I transposed from a Notebook of mine from last year when I was planning to attempt to control the Panel with a PC.
So with this I can have much faster notifications when a Zone Opens or Closes and I can also have RFID/NFC cards to Arm/Disarm if I wanted. Best part is it will be out of the Cloud.
The IT Garage 
You may not like the original schematic but the one you show here is problematic. You have the RX line going to ground.
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Glad you pointed that out, I honestly don’t know how that ground got there, think I got side tracked and meant to add a Ground BUS. I used your Schematic for a small run of 5 PCBs, Works well too.
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