I'm doing a use case diagram for a smart home system, which is centralized by a server.
Should I include the devices as an actor in the system, because the devices use services, and create triggers and actions? Or can an actor only be a person?
To the relevant definition reminded by qwerty_so, I'd like to add some more hints:
If the devices are autonomous systems that interact with the system under consideration for your use-cases, they can be actors.
If the devices are not autonomous and are controlled by your central server and are in reality a part of this system, they should not be actors, because actors are necessarily external to the system.