I'm just learning about UML and am questioning how to define actors correctly. I know that actors perform role in the system and I don't have a problem determining human actors. My question is how do I decide what non-human, external components are actors on the system.
For example, in a home automation system a homeowner and a system installer would be actors. Would it be correct to name a door sensor or a coffee maker an actor? These components receive signals from the main computer module and use cases could be written for actions taken on them (i.e. turn the coffee maker on/off).
Is the main computer/server the "system" or is the system made up of the collection of the computer/server and all of the components (lighting modules, coffee makers, door sensors)?