You can improve the reliability of stuff like this by minimizing programmability and by using reliable parts. I have a mercury thermostat in the basement set to

You can improve the reliability of stuff like this by minimizing programmability and by using reliable parts. I have a mercury thermostat in the basement set to 12C connected directly across the heat demand leads. So my house is pretty much not going to freeze down no matter what the software does. I have a mercury thermostat upstairs set to my normal indoor temperature. It is connected across the heat demand leads through a software controlled switch. So no matter what the software does, the house can not get too hot or two cold. This means that I only have two set temperatures, but in practice that is enough. Setback occurs whenever the system detects that the alarm is set or when I set it before I go to bed. The alarm panel is a traditional system in a box with a separate backup battery. It tells the automation when it is armed. It can be disarmed from the automation with a code, which the automation has to generate as a hash from an electronic key.