Halo's main weapon exists primarily in case the Flood manage to escape containment and spread their infection to other planets. John-117 noted in his debriefing of the Halo event that, if not for Cortana's intervention, he would have accidentally activated the weapon and destroyed all life in the galaxy. However, it is also possible to insert the Index into the Core without triggering the ring's main weapon and instead use the authorization provided by the Index to manage the Halo's custodial systems. While inside the Core, Cortana also had complete control over the Index itself, as she was able to remove the Index's data and store it within her system. An AI construct inside the Core is able to prevent the initiation of the ring's firing sequence even if the Index is inserted, as demonstrated when Cortana prevented John-117 from activating Installation 04.
The activation process may be aborted by physically removing the Index before the firing however, doing so sends out a signal which places the entire Array into standby mode, ready for activation from the Ark. When inserted into the Core inside a Halo's Control Room, the Index immediately initiates the charging sequence of the ring's main weapon.
Once safely in the installation's Control Room, however, the monitor must hand the Index over to the Reclaimer, as monitors are not allowed to activate their Installations by themselves. Immediately after this, however, the Index will be taken by the monitor for safekeeping to ensure it does not fall in the hands of the Flood in the event the Reclaimer is infected. Īccording to containment protocols followed by the monitors of each Installation, only a Reclaimer is allowed to retrieve the Index from the Library. Each Index is stored safely within an Index chamber, a large room that is located at the core of every Library on each Halo installation and guarded by waves of Sentinels.
The object seems to be merely a digital storage device containing the software or access codes needed to activate the rings, as shown when Cortana extracted the Index's data and stored it within her memory, and when she activated the second Installation 04 with the stored Index. The Index is vaguely T-shaped, with a faint green or blue glow emanating from a stripe on each side.
Cortana producing a hologram of Installation 04's activation index from her memory banks.