From Halopedia, the Halo wiki
An identity disk is carried by Covenant Sangheili for security purposes. The identity disk is a small diskette that is meant to be read on a handheld reader. It contains information on its holder's name, rank, etc. It is similar to the concept of the dog tag used by the UNSC Marine Corps.
They used in cases of utmost formality, such as meetings with Prophets or other members of the High Council. In this case, they are also used in coordination with the DNA slot machines, to ensure the safety of the Prophets and Council members.
List of appearances
- Halo: The Flood (First appearance)
- Halo: The Flood, chapter 3