SIM card lock: how the SIM PIN and PUK work, and how to set or remove them

What is a SIM card lock?

A SIM card lock is a PIN stored on the SIM itself. When it is on, the phone asks for the PIN every time it starts, and every time the SIM goes into another phone. Until you enter it, the SIM cannot make calls or use mobile data. Apple describes it as a way to "lock your SIM card or eSIM with a PIN" so that an identification code is needed for calls and data. It works on an eSIM as well as a physical card.

Why bother? Google's Pixel help puts it simply: if your phone is lost or stolen, "an unauthorised individual can use the SIM card in your device to control your phone number". That includes receiving the one-time passcodes your bank sends by text. A SIM PIN stops the card working in someone else's phone.

This is desk research from Apple's, Google's, Samsung's and the operators' own pages. We have not tested every phone or network listed.

SIM PIN, PUK and a carrier-locked phone: what is the difference?

Three different locks get called "SIM locked", and they need different fixes.

A message such as "SIM card is locked" or "PIN required" is the first kind. "PUK required" or "PIN blocked" is the second. "SIM not supported", or a request for a network unlock code after you insert another operator's SIM, is the third. Samsung UK explains the split clearly: the SIM PIN protects your SIM from being used in other devices, while a network unlock code locks the device to a provider. Samsung says it "does not lock any of its devices to any particular network"; the operator does.

How do I turn the SIM PIN on or off on an iPhone?

Apple's steps, from its "Use a SIM PIN for your iPhone or iPad" article:

1. Open Settings and tap Cellular.
2. With one line, tap SIM PIN. With Dual SIM or Dual eSIM, tap the number first, then SIM PIN.
3. Switch it on or off.
4. Enter your SIM PIN if asked. If you have never set one, enter the operator's default PIN.
5. Tap Done.

On a cellular iPad the path is the same: Settings, Cellular, SIM PIN. Apple's article covers switching the lock on and off; it does not describe changing the PIN.

How do I set or remove the SIM PIN on Android?

The menu names vary by maker.

Samsung Galaxy (from Samsung UK's support page): Settings, then Biometrics and security, then Other security settings, then Set up SIM card lock, then Lock SIM card. Enter the PIN and tap OK. To turn it off, tap Lock SIM card again and enter the PIN. To change it, tap Change SIM card PIN once the lock is on. Older Galaxy phones start from Lock screen and security instead.

Google Pixel (from Google's Pixel help): Settings, then Security and privacy, then More security settings, then SIM lock, then Lock SIM.

Google recommends a PIN of six or more digits, and warns that "some operators have a default PIN, which is available to the public". If you switch the lock on, change the default straight away.

What is the default SIM PIN?

It depends on the operator. Samsung UK says "the default PIN number will depend on your network provider", and that it may be printed on the SIM's original packaging; Apple says to check your provider's customer service page or the documents that came with the plan. Do not guess. Apple warns: "Don't try to guess your SIM PIN," because wrong guesses can lock the SIM.

What happens if I enter the wrong SIM PIN?

Vodafone UK's help page sets out the usual rule:

• Three wrong PINs and the SIM asks for a PUK (Personal Unblocking Key).
• Ten wrong PUKs and the SIM is permanently blocked. You then need a replacement SIM.

The PUK comes from your operator, not from Apple or Samsung. Vodafone says to contact its customer services and ask for a PUK code. Apple's advice matches: "Never try to guess a SIM PIN or Personal Unlocking Key (PUK) code", and if you see "PUK exhausted", ask your provider for a new SIM card or eSIM. Our SIM card replacement page covers that.

How do I unlock a carrier-locked phone?

Only the operator that locked it can unlock it. Apple says the same of iPhones: "Only your current carrier can unlock your iPhone," and the request might take a few days.

• Check first. On an iPhone, go to Settings, General, About. Apple says that if it shows "No SIM restrictions" next to Carrier Lock, the phone is unlocked.
• Ask the operator. Vodafone UK, for example, takes network unlock code requests through an online form and says unlocking a Vodafone phone or SIM is free.
• Then insert the new SIM or set up the new eSIM, and the phone activates.

An unlocked phone matters for travel: a locked phone will not accept a local SIM or most travel eSIMs. Our eSIM iPhone and eSIM Android guides cover setup once it is unlocked.

Blocking a lost SIM is different

Many searches for "SIM block", especially for Airtel and Jio, are about something else: stopping a lost or stolen SIM from being used. That is not done with a PIN; your operator blocks the number. Airtel's guide gives three routes that do not need a call: live chat in the Help section of the Airtel Thanks app, email to Airtel support, or an Airtel store with original ID, where the agent can also issue a replacement with the same number. We did not read Jio's own page on blocking a lost SIM, so contact Jio directly or visit a Jio Store. Turning on a SIM PIN beforehand is what stops a thief using the card before you get it blocked.

Should you lock your SIM card when travelling?

Yes, if you keep your home SIM in the phone abroad. A stolen phone with an unlocked SIM gives the thief your number and your bank's texts. Set a SIM PIN before you go, note it somewhere other than your phone, and keep the operator's PUK details to hand. If you use a travel eSIM for data, you can lock that too; Apple's and Google's settings apply to each line. Our SIM card not working page helps if the phone still will not connect after you enter the PIN.