Can be relatively simple inside of Home Assistant. I have my alarm attached to Konnected, and that has an HA integration. I can both arm and disarm my alarm through an HA dashboard, and also have it arm itself if both myself and the wife are out of the house. You may not even need the alarm integration part- you can just use the home/away functionality and set the thermostat. The thermostat integration part I am less sure about, just because I haven't used it, but it should be fairly easy to set the set temps based on your home/away status.

Of course you need Home Assistant set up for this, but if you are interested in these types of things, it will be very useful.