Gas (methane) detector (and ideally smoke and co detectors) with alert on app (and on site)

I don’t know for sure with that particular model. Typically with Shelly, there are two different ways to integrate It with smartthings.

The official integration is cloud to cloud. You add it to your Shelly account and then you link your Shelly account to your smartthings account through “Linked services.” But that doesn’t work for all models or all features, so you need to check with Shelly support to see if the model you’re interested in is included in the official integration.

If it’s not, and you have a Smart thinka/Aeotec hub, there is a community integration that might work. Again, check that thread to see if that specific model has been included yet.

Edge Shelly drivers for Gen1 and Gen2 Devices