Exclusive Chip Identification (ECID)

A 64-bit identifier that’s unique to the processor in each iOS and iPadOS device. When a call is answered on one device, ringing of nearby iCloud-paired devices is terminated by briefly advertising through Bluetooth Low Energy (BLE) 4.0. The advertising bytes are encrypted using the same method as Handoff advertisements. Used as part of the personalization process, it’s not considered a secret.