I was wondering if anyone has tried integrating the new Shelly wifi devices into smartthings? https://shelly.cloud/
There is a rest API, and as they are ESP8266-based there is also the possibility of flashing new firmware (similar to Sonoff devices) and bypassing the Shelly cloud altogether. In particular the Shelly 1 relay is very compact and could be useful for installing in switch boxes and/or a ceiling rose. the smoke detector also looks like it could be good.