Smart homes are a new idea, and as such, the meaning of the term varies. So when trying to talk about them, it's good to check and make sure you and the person you are speaking with are thinking of the same thing.
In general, "smart homes" are houses that have several building automation solutions implemented in them, allowing the house to be controlled from the convenience of a single user interface. The interface in question can take many forms, from a tablet mounted on the living room wall to smart speakers like Amazon's Alexa, which allows the house to be controlled via voice commands. Cellphones are often used as control units as well.
Pretty much any system and appliance in a person's house can be automated and integrated with the house's smart setup. Common targets are lamps, climate control systems, kitchen appliances, and the house's security systems - including locks, alarms, and cameras.
The backbone of a smart home implementation is the IoT hardware being used. That will determine how comprehensive and how reliable the smart setup is going to be, and the best way to acquire good IoT hardware is to have it custom designed and produced to suit your needs by a team of professionals. This company
, for example, can handle that type of service.