A Personal Unlock Code (PUC), also known as a PIN Unlocked Key (PUK), is used in GSM mobile phones (phones with a SIM card). Most mobile phones offer personal identification number (PIN) protection. After switching on the phone, if the PIN security function is active, you can enter a 4-8 digit PIN enabling the phone's non-emergency calling functions. If the wrong PIN is typed in more than three times, either the SIM card, the phone or both become locked. They can be unlocked by entering a PUC, provided by your service operator through verification.

NOTE: If the wrong PUC is entered ten times in a row, the device will become permanently blocked and unrecoverable, requiring a new SIM card. You should keep PUC written down in a safe place separate from the phone.

The PUC (PUK) is a SIM-specific code assigned by your service provider. If you do not know your PUC and you are prompted for it, contact your service provider. Once you enter the PUK code, you must set a pin. The PUK (Personal Unblocking Key) and PUK2 are used to unlock the PIN and PIN 2 codes respectively if your SIM card is blocked.