I have removed one of the 2 Xiaomi Mijia Honeywell Smoke Detectors from my SmartThings hub to test pairing for you.
Start pairing mode in the App (Classic app) and press the button on the front of the smoke detector repeatedly every 1 seconds. Continue until you see the message that a new Thing is found.
Accept that device and press Save. Go to IDE via a web browser and install the DTH.
I had the DTH from bspranger already installed when I tested pairing.
Grtn Ben
