The device registry is a registry where Home Assistant keeps track of devices. A device is represented in Home Assistant via one or more entities. For example, a battery-powered temperature and humidity sensor might expose entities for temperature, humidity and battery level.
A device in Home Assistant represents a physical device that has its own control unit. The control unit itself does not have to be smart, but it should be in control of what happens. For example, an Ecobee thermostat with 4 room sensors equals 5 devices in Home Assistant, one for the thermostat including all sensors inside it, and one for each sensor. Each device exists in a specific geographical area, and may have more than one input or output within that area.
If you connect a sensor to another device to read some of its data, it should still be represented as two different devices. The reason for this is that the sensor could be moved to read the data of another device.
A device that offers multiple endpoints, where parts of the device sense or output in different areas, should be split into separate devices and refer back to parent device with the
via_device attribute. This allows the separate endpoints to be assigned to different areas in the building.
Although not currently available, we could consider offering an option to users to merge devices.
|id||Unique ID of device (generated by Home Assistant)|
|name||Name of this device|
|connections||A set of tuples of |
|identifiers||Set of identifiers. They identify the device in the outside world. An example is a serial number.|
|manufacturer||The manufacturer of the device.|
|model||The model of the device.|
|config_entries||Config entries that are linked to this device.|
|sw_version||The firmware version of the device.|
|via_device||Identifier of a device that routes messages between this device and Home Assistant. Examples of such devices are hubs, or parent devices of a sub-device. This is used to show device topology in Home Assistant.|
|area_id||The Area which the device is placed in.|
|entry_type||The type of entry. Possible value is |
Entity device info is only read if the entity is loaded via a config entry.
Each entity is able to define a device via the
device_info property. This property is read when an entity is added to Home Assistant via a config entry. A device will be matched up with an existing device via supplied identifiers or connections, like serial numbers or MAC addresses. If identifiers and connections are provided, the device registry will first try to match by identifiers. Each identifier and each connection is matched individually (e.g. only one connection needs to match to be considered the same device).
Components are also able to register devices in the case that there are no entities representing them. An example is a hub that communicates with the lights.