"No SIM card", "SIM not detected" or "Invalid SIM" can appear suddenly, and without a SIM you have no calls, texts or mobile data. The cause can be as simple as a dusty tray or as serious as a carrier lock or damaged reader. Work through these fixes in order.
1. Restart the phone
A restart forces the modem to re-read the SIM. It fixes more cases than you'd expect.
2. Toggle Airplane mode
Turn Airplane mode on for 15 seconds, then off. This resets the mobile radio.
3. Reseat the SIM card
- Power off the phone.
- Eject the SIM tray with the ejector tool.
- Check the SIM for scratches, dirt or bending.
- Wipe the gold contacts gently with a dry microfibre cloth.
- Make sure the SIM sits flat and correctly oriented in the tray.
- Reinsert fully and power on.
Avoid DIY-cut SIMs (e.g., trimmed nano SIMs); poorly cut edges often cause detection issues.
4. Test the SIM in another phone (and another SIM in yours)
- SIM fails in another phone too: the SIM is faulty or deactivated. Ask your carrier for a replacement.
- Another SIM works in your phone: the issue is your SIM or account.
- No SIM works in your phone: likely a phone setting, lock or hardware issue.
5. Check SIM settings
Android: Settings → Network & internet → SIMs → make sure the SIM is turned on (dual-SIM phones can disable a slot).
iPhone: Settings → Mobile Data (Cellular) → check the line is on and labelled correctly.
6. Update software and carrier settings
- Install system updates.
- iPhone: Settings → General → About. A carrier settings update prompt may appear.
Photo by Andrey Matveev on Pexels
7. Reset network settings
- Android: Settings → System → Reset options → Reset Wi-Fi, mobile & Bluetooth.
- iPhone: Settings → General → Transfer or Reset → Reset → Reset Network Settings.
This clears APN and network settings without deleting personal data.
8. Check for a carrier lock
If a new carrier's SIM shows "Invalid SIM" or "SIM not supported", your phone may be carrier-locked. Contact the original carrier for an unlock (usually free once the contract is paid).
9. eSIM phones
On eSIM-only or dual phones, make sure the eSIM profile is active and not deleted. If you changed phones, you may need a new eSIM transfer or QR code from the carrier.
10. Hardware problems
Signs of a hardware fault:
- No SIM is detected at all, even new ones
- Problem started after a drop or water exposure
- The SIM tray is bent or loose
A repair shop can test the SIM reader or signal board. Check warranty first.
Quick checklist
| Step | Fixes |
|---|---|
| Restart / Airplane mode | Temporary modem glitches |
| Reseat and clean SIM | Poor contact |
| Swap SIMs | Identifies SIM vs phone |
| Network reset | Corrupt network settings |
| Carrier unlock | "Invalid SIM" after switching |
| Repair | Damaged reader |
Video fixes
Summary
Restart, reseat and clean the SIM, test it in another phone, reset network settings, and check for carrier locks. Most "SIM not detected" errors are fixed before you need a repair.
Switching carriers often? Choose an unlocked phone with eSIM support. See infozme's latest mobiles page.
Cover photo by Andrey Matveev on Pexels. This article was written with the help of AI.
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