"No SIM", "SIM not detected" or "Invalid SIM"

The phone cannot read the SIM. A dirty or shifted card is the usual cause; a worn-out SIM comes next.

What you seeNo SIM / Insert SIM card / SIM not detected / Invalid SIM / SIM failure

1. Restart, then reseat

1. Restart the phone. Sometimes that is all.
2. Switch it off and take out the SIM tray with the ejector pin (push straight into the small hole beside the tray, not into the microphone hole).
3. Look at the card. The gold contacts should be clean and unscratched. Wipe them gently with a dry soft cloth or a pencil eraser, and blow away the crumbs.
4. Check the tray: is it bent or cracked? Does the card sit flat, in the cut-out that matches its clipped corner?
5. Push the tray in until it is flush and switch on.

A SIM that has been cut down from a larger size, or sits in an adapter, often shifts or catches. Operators replace such cards with a proper nano SIM.

2. Try the other slot, and the swap test

• On a dual-SIM phone, move the SIM to the other slot. If it works there, the first slot's reader is faulty.
• Put the SIM in another phone. Not detected there either: the SIM is dead. Get a replacement with the same number from the operator's store; take identity proof.
• Put a different SIM in your phone. If that is not detected either, the phone's SIM reader is faulty: service centre.

3. Check settings

• Flight mode off.
• Android: Settings › Network & internet › SIMs: is the SIM listed, and is "Use SIM" on? Samsung: Settings › Connections › SIM manager.
• iPhone: Settings › Mobile Service. If the line is listed but off, turn it on.
• Install any pending system update. On iPhone, also accept a Carrier Settings Update if offered (Settings › General › About).
• Reset network settings (see no network, step 7).

4. "Invalid SIM" or "SIM not supported"

This message is different: the phone reads the card but refuses it.

• A locked phone. Phones bought on contract abroad, and some bought from an operator, accept only that operator's SIMs until unlocked. The original operator does the unlocking; unofficial "unlock" services are risky.
• A deactivated SIM. Numbers left without recharge beyond the operator's limit are switched off and eventually given to someone else. Ask the operator quickly.
• A blocked handset. A phone reported lost or stolen is barred from networks. For a second-hand phone, check its IMEI on the government's Sanchar Saathi portal before buying.

5. "SIM locked", "Enter PUK"

If a SIM PIN was entered wrongly three times, the SIM locks and asks for a PUK code. Do not guess: ten wrong PUK attempts destroy the SIM. Get the PUK from the operator's app, website or customer care after identity verification.

6. eSIM not working

• Settings › the eSIM line: turn it off and on, then restart.
• Do not delete the eSIM to "fix" it. A deleted eSIM cannot simply be re-added; the operator has to issue a new QR code or activation.
• Check that the plan is active with the operator.
• If the eSIM vanished after a reset or a repair, the operator must reissue it.

7. After a drop or water

A knock can unseat the SIM or crack the reader's pins; liquid corrodes the contacts. Dry the tray and slot (see water damage) and reseat. If the fault remains, it is a repair.

Look after the SIM

Handle the card by its edges, keep it away from magnets and heat, and do not swap it between phones more than needed: the contacts wear. A SIM more than several years old that starts failing now and then should simply be replaced. The number stays the same.

While you are without the SIM

Calls and SMS, including bank OTPs, will not reach you. WhatsApp and other internet apps keep working on Wi-Fi with your existing login. Sort it out promptly if you rely on OTPs. See OTP not received.

For Android phones and iPhones. Written in November 2026 for Android 13 to 15 and iOS 17 and 18. Phone makers rename menus; use the search box in Settings if a name differs. Back up before any reset. This is an independent guide, not connected with Google, Apple, Samsung or any phone maker or operator.