How To Set Up SIM Card Lock On Android And iPhone (Step-By-Step Guide)

What happens when someone pops your SIM card out of your phone and slips it into theirs? Spoiler: if you haven’t locked it, they suddenly own your number. That means your calls, texts, and even those fragile SMS-based two-factor authentication codes are now in their hands.

A SIM Card Lock (also called a SIM Lock or SIM Lock Code) stops that from happening. It’s like putting a padlock on your digital identity. Once enabled, your SIM demands a PIN every time the phone restarts or when the card is inserted into another device. 

Without it, even the most secure phone service in the world can’t protect you from a thief with a paperclip and 30 seconds.

Before diving into setup, let’s clear up the three “locks” that often get mixed together:

• Device Lock (Passcode/Biometrics): Protects your apps and data. If your phone gets snatched, Face ID, a fingerprint, or a passcode keeps strangers out of your photos and messages.
• SIM Card Lock (PIN/Code): Protects your number itself. Even if someone moves the SIM into another phone, they can’t use your plan without entering the PIN.
• Carrier Lock: Limits what network a phone can run on. This is more about business contracts than personal security and doesn’t stop a SIM-swap attack.

For our purposes, the SIM Card Lock is the one you want. It protects your number against SIM swapping; a fraud tactic where attackers convince your carrier to transfer your line to their own SIM. 

Even if they succeed at the carrier level, a locked SIM demands a code before it connects.

Apple made SIM management fairly straightforward. Whether you use a physical SIM or eSIM, the steps are identical.

Steps to enable SIM Lock on iPhone:

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1. Open Settings.
2. Tap Cellular (sometimes called Mobile Data).
3. Choose SIM PIN.
4. Toggle the switch on.
5. Enter the default SIM PIN (check your carrier docs; never guess).
6. Tap Done.

Once enabled, you can also change the PIN to something memorable but not obvious (no birth years, no “1234”).

Quick tips for iPhone users:

• You’ll need to re-enter the PIN each time your phone reboots.
• Don’t enter it wrong three times in a row, or the SIM will demand a PUK code from your carrier.
• If you run dual SIMs, repeat the process for each line under “SIMs.”

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Watch this video for more information:

On Android, the process looks a little different depending on whether you’re using stock Android (like Google Pixel) or a custom skin (Samsung, OnePlus, etc.). 

But the core idea is the same: find “SIM card lock” in Settings and toggle it on.

Steps on stock Android (Google Pixel, etc.):

1. Open Settings.
2. Scroll to Security & Privacy.
3. Tap More Security Settings.
4. Choose SIM Card Lock.
5. Select the SIM you want to secure (if dual SIM).
6. Toggle Lock SIM Card on.
7. Enter your carrier’s default PIN.

Steps on Samsung (One UI):

1. Open Settings.
2. Tap Biometrics and Security.
3. Go to Other Security Settings.
4. Tap Set Up SIM Card Lock.
5. Switch it on, then enter the default SIM PIN.

After setup, change your SIM PIN:

• Tap Change SIM PIN.
• Enter the old PIN once, then the new PIN twice.
• Save and remember it.

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Default SIM Pin Codes of Popular Mobile Carriers

Most U.S. carriers ship SIM cards with weak, predictable default PINs like 1111 or 1234. If you haven’t changed yours, it’s likely still one of these.

Below are the defaults for the most popular carriers and their MVNO families:

• Verizon Wireless — 1111
  
• AT&T — 1111
  
• T-Mobile — 1234 (sometimes 0000 or 5678 on older SIMs)
  
• Cricket Wireless (AT&T) — 1111
  
• Metro by T-Mobile — 1234
  
• TracFone (Verizon SIMs) — 1111‍
• Visible (Verizon) — 1111

Here’s the catch: you only get three attempts. After that, the SIM enters a locked state and demands a PUK code.

• PUK Code (Personal Unblocking Key): An 8-digit code provided by your carrier. Usually printed on the original SIM card packaging or retrievable from your carrier account.
• Ten wrong PUK attempts = dead SIM: At that point, the card is permanently disabled, and you’ll need a new one.

So: don’t guess. Always confirm the default SIM lock code with your carrier before entering anything.

Some people skip SIM locks because they can be annoying; you have to type in the PIN every time you restart. But here’s why it’s still smart:

• Stops SIM Swapping Cold
  Even if scammers trick your carrier, the stolen SIM is useless without the PIN.
• Protects Your Number
  Texts, calls, and one-time passcodes can’t be hijacked.
• Adds A Layer Beyond Carrier Security
  Even with a secure cell phone service, your PIN is your personal safeguard.
• Works With eSIMs Too
  Even though eSIMs can’t be physically removed, the PIN still matters if someone tries to reset or transfer the profile.

Think of it as a lock on your mailbox. Sure, you might check it daily, but without that lock, anyone could open it first.

Setting up a SIM Card Lock takes two minutes and saves you from a nightmare scenario where an attacker hijacks your number. Whether you’re on Android or iPhone, don’t confuse it with your screen lock or a carrier lock; it’s its own separate shield.

Also, Read: How Do I Know If My Phone Is Unlocked?

How Do I Lock My SIM Card On iPhone?
Go to Settings > Cellular > SIM PIN, toggle it on, and enter your carrier’s default code. After that, change it to something unique.

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How Do I Lock My SIM Card On Android?
Open Settings > Security & Privacy > More Security Settings > SIM Card Lock. Toggle it on and enter the default code. Samsung users will find it under Biometrics and Security > Other Security Settings > Set up SIM card lock.

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What Is A SIM Lock Code?
It’s the PIN that secures your SIM card from being used in another phone. Without it, anyone who has your SIM could hijack your calls and texts.

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What Happens If I Forget My SIM PIN?
You’ll need the PUK code from your carrier to reset it. Entering the wrong PUK too many times permanently disables the SIM.

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Does A SIM Lock Work With eSIM?
Yes. Even though eSIMs can’t be physically removed, the SIM lock still prevents unauthorized use if someone resets or transfers the eSIM profile.