A code cylinder, or data cylinder, was a common security device used by military officers, corporate executives, and politicians. It acted as a sophisticated keycard for secure areas. Each cylinder contained its user's personal security clearance codes and data. It was not uncommon for high-ranking personnel to own multiple code cylinders, each with their own encrypted access codes. They were used extensively in the Galactic Republic, Galactic Empire, and New Republic, particularly to facilitate security measures. The devices, usually carried within a pocket or on one's belt, used the same interface as a droid's scomp link.
Additionally, code cylinders could be reprogrammed. In situations where it was impossible for a slicer to be physically present and hack a security door, they sometimes elected to reprogram the cylinder instead. Cylinders were programmed with countermeasures such that a failed reprogramming caused the data to become irretrievably corrupted.
Within the Imperial Navy, code cylinders were also utilized as rank identifiers. In the case of flag officers, it related to their fleet responsibilities. New code cylinders were typically issued with every new assignment, and the officers did not normally wear them when not on active duty. They were worn in small pockets near the shoulders of the uniform tunic, with the first always placed on the left-hand pocket near the rank plaque. Those in specialist positions in the Imperial Navy also had access to them, although in their case, they served purely as insignia.
During the Jedi Civil War, the Sith officer Commander Doel Scherp was entrusted with a code cylinder that contained the command codes for the sensor systems of Darth Revan's flagship. In approximately 3957 BBY, a team of Republic agents stole the code cylinder from Scherp's Estate on the planet Sernpidal, and took the device to a rendezvous point with the Republic Fleet, on the Republic's border with the Sith Empire. The Fleet subsequently used the information contained within the cylinder to attack the flagship, and capture Darth Revan.