5.7. Non-Visual Code Transmission

There is no requirement that the user code be displayed by the device visually. Other methods of one-way communication can potentially be used, such as text-to-speech audio or Bluetooth Low Energy. To mitigate an attack in which a malicious user can bootstrap their credentials on a device not in their control, it is RECOMMENDED that any chosen communication channel only be accessible by people in close proximity, for example, users who can see or hear the device.