The device commonly used as a central unit in smart home automation is a smart hub. A smart hub serves as the cohesive control center for various connected devices within a smart home. It facilitates communication between devices that use different protocols, such as Zigbee, Z-Wave, and Wi-Fi, allowing for seamless integration and automation. Users can manage their smart home systems through a single interface, utilizing apps or voice commands, thereby enhancing convenience, energy efficiency, and security in daily living.