The Personal Unblocking Key (PUK) is an eight-digit code required to reset a locked SIM card. This situation typically arises when the incorrect Personal Identification Number (PIN) has been entered multiple times. On an Android device, the prompt to input this code appears automatically when a SIM card lock is triggered due to repeated incorrect PIN attempts. This prompt usually displays a clear field for entering the code and instructions to obtain the PUK from the mobile carrier.
The ability to unlock a SIM card using this mechanism is crucial for maintaining uninterrupted mobile service. Without the correct key, the SIM card becomes permanently unusable, requiring a replacement. This process safeguards against unauthorized access to the mobile network in case of a lost or stolen device. The implementation of this security measure has evolved alongside the development of SIM card technology, becoming a standard feature across various mobile operating systems.