What type of device twin property is not visible to the device itself?

The concept of device twin properties in Azure IoT Hub distinguishes between different types of data that are important for managing device behavior and state. Tags are considered metadata for a device twin and are utilized for organizing and categorizing devices, but they are not directly accessible or visible to the device itself. Instead, tags are typically used for device management and can be used in queries or to group devices logically.

By contrast, desired properties are configurations or settings that can be changed from the cloud to influence the device's operation, and reported properties are the device’s state or telemetry data that the device sends back to the cloud. Both desired and reported properties can be accessed by the device, as they are directly involved in the communication between the device and Azure IoT Hub. Identity properties, which include unique identifiers and authentication information, are also part of the device twin but are more associated with the IoT Hub’s management of the device rather than the device's operational abilities.

In summary, while tags are useful for administrative purposes and organization within the Azure platform, they remain invisible to the device, fulfilling a backend role rather than an interactive one with the device itself.