Use device classes

This is a Gold rule. In quality_scale.yaml, it is called entity-device-class.

Entities use a device class wherever one fits. A temperature sensor uses SensorDeviceClass.TEMPERATURE, a door contact BinarySensorDeviceClass.DOOR, a firmware update UpdateDeviceClass.FIRMWARE. The entity pages list the device classes of each platform.

A device class tells Home Assistant what an entity measures or represents, and a lot builds on that:

• Users can switch a sensor to another unit, like from °C to °F, only when the device class is known.
• Assist can answer "what is the temperature in the living room?".
• Google Assistant and Amazon Alexa know how to expose the entity.
• The frontend picks a fitting icon, and shows the state in the right way, like "Open" instead of "On" for a door.
• Entities can be named after their device class, so they need no translation of their own.

This sensor uses the temperature device class. It has no name of its own, so it is named after the device class: "My device Temperature".

class MyTemperatureSensor(SensorEntity):
    """The temperature of My device."""

    _attr_has_entity_name = True
    _attr_device_class = SensorDeviceClass.TEMPERATURE
    _attr_native_unit_of_measurement = UnitOfTemperature.CELSIUS

    def __init__(self, device: MyDevice) -> None:
        """Initialize the sensor."""
        self._attr_unique_id = f"{device.serial}_temperature"
        self._attr_device_info = DeviceInfo(
            identifiers={(DOMAIN, device.serial)},
            name="My device",
        )

• Pylint warns when a translation key only repeats the name the device class already provides (home-assistant-redundant-translation-key).
• Whether a device class fits, and whether one is missing, is checked in review.

If the integration has no entities, or its entities are on platforms that have no device classes, like light, tts, or conversation, this rule does not apply.

• has-entity-name: use has_entity_name.
• entity-translations: translate entity names.
• icon-translations: use icon translations.