SIM PIN explained: what it protects and how to set one

Most people think of their phone number as just a way to be called. It’s also a key. Banks, email providers and social accounts send sign-in and reset codes to it by text. Whoever holds your SIM can receive those codes, which is why a stolen phone is sometimes worth less to a thief than the SIM inside it.

What a SIM PIN does

A SIM PIN is a short code stored on the SIM card itself, or on the eSIM profile. When it’s turned on, the SIM locks every time the phone restarts or the card is moved to another phone. Until someone types the PIN, the SIM can’t make calls, use mobile data or receive texts. Your phone shows a locked SIM in the status bar.

That matters in one specific situation: someone takes your phone, pops out the SIM and puts it in a phone they control. Without a SIM PIN, your texts start arriving there, including the codes that reset your passwords. With a SIM PIN, the card stays locked and useless to them.

What it doesn’t do

• It doesn’t lock the phone. That’s your screen lock’s job. The SIM PIN only guards the SIM.
• It doesn’t stop a SIM swap at the carrier. In a SIM swap, a scammer convinces your carrier to move your number to a new SIM. Your PIN is on the old card, so it can’t help. Ask your carrier about an account PIN or port-out protection for that.
• It doesn’t help while the phone is on and unlocked. The SIM stays unlocked until the next restart, so a phone snatched from your hand still receives texts.

For that last case, theft protection features help more. See Android theft protection explained, and on iPhone, the guide to Stolen Device Protection.

Before you start: find the default PIN

Every SIM comes with a PIN set by the carrier, even if it’s switched off. You need it to turn the lock on. Look on the card holder the SIM came in, in your plan’s paperwork or on the carrier’s help pages. Don’t guess. A few wrong tries locks the SIM and asks for a PUK code, and too many wrong PUK tries can block the SIM for good.

Once the lock is on, change the default to a code of your own. Many carriers use the same default for every customer, so a SIM still on its default PIN isn’t really protected.

Turning it on

On iPhone:

1. Open Settings and tap Cellular (or Mobile Data in some regions).
2. If you have more than one line, tap the number you want to protect.
3. Tap SIM PIN and turn it on.
4. Enter the current PIN, then tap Done.

You can then use Change PIN on the same screen to choose your own.

On Android: the setting has a different name and place on different phones. Search Settings for “SIM lock” or “SIM PIN”. It’s usually under security or under the mobile network settings. Turn on the option to lock the SIM, enter the carrier’s default PIN, then use the option to change the PIN.

If you forget it

If your phone asks for a SIM PIN you don’t know, stop and don’t guess. Contact your carrier. They can give you the PUK code, which unlocks the SIM and lets you set a new PIN. If the PUK attempts run out, the carrier will need to issue a new SIM or eSIM.

Write your SIM PIN down somewhere safe, away from the phone. You’ll only need it after a restart, which is exactly when people forget it.

Is it worth it?

For most people, yes. It costs one extra code after each restart, and it closes off a quick route from a stolen phone to your accounts. It’s most worth doing if:

• your bank or email still sends codes by text
• you travel or commute with your phone in crowded places
• your phone number is widely known, such as for work

Moving important accounts away from text codes, toward an authenticator app or passkeys, protects you even more, because then your number stops being a key at all.

How Silo relates

Silo, coming soon to iPhone and Android, has no account and no phone number attached, so there’s no code to intercept and nothing to reset by text. Its vault opens with its own PIN, separate from your phone and SIM.