Have you seen this device and the custom handler @krlaframboise made?
[OBSOLETE] GoControl/Linear Multifunction Contact Sensor
I don’t have one but in that thread it seems like the DTH can handle internal and external contacts simultaneously? It may even be able to tell you locked/unlocked vs. open/closed with some edits to the code.
This is a healthy attitude to have when getting started with ST as a security system. It’s not just the DIY-nature of it (which can be fun), but the unreliability/cloud gremlins/whatever that make it a poor option for more serious security needs.
Unfortunately I feel the same way about Blink overall too. Convenient for notifications, sure. But they have a ways to go before they can meet the standards of a more professional security system too.