As of this writing Smartthings allows you to create a “simulated presence sensor” Which is a virtual device that you can turn on and off with other conditions occurred.
So there are indeed some people who use check ins to their own Wi-Fi system for presence detection. Others, like myself, need an even smaller geopresence region. So I use an IBeacon combined with IFTTT.
Others use other methods.
There is a community FAQ about this, but all of the examples are from the old version of the app, so at this point it’s more of a proof of concept topic then a specific how to. But it can definitely be done.