This visualization of a home automation shows a mesh network of smart switches, smart plugs, and sensors.

The rectangle object in the diagram identifies a Zigbee Coordinator (radio adapter) which is the go-between for the automation hub. Sensor end devices (circular object) that are within close proximity can signal back to the Coordinator directly. Data is transmitted using a low power RF so signal strength is a factor. Happily, since this is a mesh network, the more distant end devices can chain relay through smart devices (oblong object) which relay amplify to the Coordinator like a router.