Before you can register something, you must understand what it is. ECID stands for (sometimes referred to as Electronic Chip ID).

For the average iPhone user, the acronym "ECID" likely means nothing. It is buried deep within the technical architecture of the device, invisible to the daily user interface. However, for the jailbreak community, security researchers, and power users, the ECID is the single most important identifier for maintaining control over their device.

Click on the field multiple times until it changes to show your ECID .