Command neural interface
From Halopedia, the Halo wiki
Command Neural Interface implants are implanted in the brains of every UNSC ship commander. In addition to the duties of a standard Neural Interface, they also have several purposes specific to a ship commander.
Once installed, they cannot be removed without killing the host, and are permanent. Their main use is the storage of data codes, NAV data, and also for receiving telemetry from outside sources. AIs can access the lace with the owner's consent, and retrieve data for use. The owner of the lace can also receive data about the ship they command, sent directly to their retenas courtesy of the shipboard AI. The CNI Transponder of the commanding officer is the only thing with clearance for initiating a vessel's auto destruct. This way, the only way a ship may be destroyed is if its commander authorizes the destruction, or if the commander is dead, their interface may be removed. Although permanent, they can be upgraded for specialized functions, such when as the Master Chief's CNI was upgraded in The Fall of Reach.
In the level Keyes, the Master Chief recovers the CNI transponder from the body of Captain Keyes, whose Flood-infested form had to be killed to retrieve them.
