Guide Scams and phishing
SIM swap scam: your phone suddenly has no signal – what to do
Your phone suddenly shows “No service” or “SOS only”, maybe right after someone called claiming to be your mobile carrier and asked for a code from a text message. That's the classic sign of a SIM swap: a criminal has moved your phone number to a SIM or eSIM they control. From then on, your calls and verification texts go to them – including codes from your bank and email. The FBI's Internet Crime Complaint Center received 1,611 SIM swapping complaints in 2021 alone, with more than $68 million in losses. Here's how to spot it, what to do in the first minutes and how to protect your number.
Key points
- In a SIM swap, a criminal gets your carrier to move your number to a SIM or eSIM they control. Your phone loses service and your calls and texts – including one-time codes – go to them.
- A common way in is a call from your “carrier” about an upgrade to eSIM or an expiring SIM, followed by a request to read out a code from a text. Never do that – the code authorises the move.
- Phone dead after a call like that? Contact your carrier immediately from another phone, then your bank, then secure your email from another device.
- Prevention: add a PIN or passcode to your mobile account, and use an authenticator app or security key instead of text codes where you can – a SIM swap can't steal those.
How a SIM swap works
Your phone number lives on a SIM card or an eSIM. Your carrier can move the number to another SIM – that's how you get a replacement when your phone is lost. Criminals abuse exactly that process. The FBI describes three ways in: social engineering (pretending to be you and tricking the carrier), a bribed or careless insider at the carrier, and phishing.
The code in that text isn't a “confirmation for the carrier”. It's a one-time password that approves moving your number to a new eSIM. The criminal starts the request themselves – for example in your carrier's online account or app – and only needs that code from you. In a case published by the Czech Police in July 2025, a woman posing as a carrier employee talked victims into reading out codes, activated eSIMs through the carrier's self-service and then, overnight, raised banking limits, applied for loans and moved the money. She got over CZK 16 million before police caught her with the carrier's help.
Not every SIM swap involves a call to you. The FTC describes the other common route: the criminal calls your carrier, claims your phone was lost or damaged, and asks to activate a SIM linked to your number on a device they control. You may notice nothing until your phone goes dead.
How to spot it
Warning signs before it happens:
- A call about a SIM change you didn't ask for – “your SIM is expiring”, “we're upgrading you to eSIM”, “your number will be disconnected today”.
- They ask for a code from a text, or for your account PIN, date of birth or ID number.
- The caller knows your name and address. That proves nothing – those details are easy to find or buy.
- The number on screen looks like your carrier's. Caller ID can be faked – more on that in Bank impersonation scam calls.
Warning signs that it has already happened (the FTC lists the first two):
- Your phone suddenly has no service – no calls, texts or data – while people around you are fine.
- A message from your carrier that your SIM or number was activated on a new device.
- Emails about password resets or new sign-ins you didn't start – check them on another device.
Your phone has lost service. What now?
If you've read out a code, or your phone suddenly shows “No service” or “SOS only” after a strange call, act now. Criminals work fast; in the Czech case, they used the night.
- Contact your carrier from another phone – a family member's, a neighbour's, a landline – or through its website on a computer. Say your number has been taken over by a SIM swap and ask them to block the new SIM or eSIM and give you your number back. The FTC's first piece of advice is to contact your provider immediately to take back control of your number.
- Call your bank on the number on the back of your card or on its official website. Ask them to block online banking and cards, and check recent payments, limits and any loan applications in your name.
- Secure your email first, then other accounts. From another device, change your email password, sign out unknown devices and check for new forwarding rules – email is the key to resetting everything else. Step by step: Someone hacked my account.
- Report it. The FBI advises victims to contact their carrier, change passwords, alert their financial institutions and report to local police and IC3 at ic3.gov. In other countries, report it to the police or your national fraud reporting service. Note when and from which number you were called, what you said and which texts arrived.
- Watch for identity theft. If the criminal also got your Social Security, card or bank account number, the FTC points to IdentityTheft.gov for a recovery plan. If they have a copy of your ID, see I sent a photo of my ID to a scammer.
- Once your number is back, switch important accounts from text codes to an authenticator app or a security key – how: Two-step verification: how to turn it on.
How to protect your number
- Add a PIN or passcode to your mobile account. The FTC says it can help protect your account from unauthorised changes; your carrier's website explains how. Ask whether it offers extra protection against SIM changes or number transfers.
- Use an authenticator app or a security key instead of text codes for your bank, email and social media where the service allows it. The FTC and the FBI both recommend this – a SIM swap can't steal an app or a key.
- Never share codes from text messages, and don't call back the number that called you. If in doubt, contact your carrier through its app or the number on your bill – the FBI's advice for anyone claiming to be your carrier.
- Keep personal details off public profiles. The FTC warns that your name, address and phone number help criminals answer security questions; the FBI adds not to talk about your financial assets, including cryptocurrency, online.
- Change SIM or eSIM only yourself, in your carrier's app or store – never because someone called you.
- Tell older relatives: “Your carrier never asks for a code from a text. If someone does, hang up and call me.”
Got a text with a link to “activate your eSIM” instead of a call? Check it before you open it with the link checker. Similar tricks where someone poses as a company you trust: NFC relay scam: “hold your card to the phone” and I entered my details on a phishing site.
FAQ
My carrier called and said my SIM must be switched to eSIM. Is it a scam?
If you didn't ask for it, almost certainly. The person on the phone wants the one-time code your carrier texts you, because that code approves moving your number to a new eSIM. Hang up and contact your carrier through its app, website or the number on your bill. Verifying the caller by calling your carrier yourself is exactly what the FBI recommends.
My phone suddenly says “No service”. How do I know it's a SIM swap?
The FTC lists two signs: your phone suddenly loses service – no calls, texts or data – and you get an unexpected notice from your provider that your SIM was activated on another device. If either happens, especially after an odd call or text about your SIM, treat it as a SIM swap and call your carrier from another phone right away. Restarting the phone won't help.
Why do criminals want my phone number?
Because many services send password reset links and one-time codes by text. The FBI explains that once criminals control your number, they receive your calls and texts, reset your passwords and intercept those codes to take over online accounts – bank, email, cryptocurrency and social media.
How do I protect my number from a SIM swap?
Ask your carrier to add a PIN or passcode to your account – the FTC says it can help protect it from unauthorised changes. For important accounts, switch from text codes to an authenticator app or a security key, as both the FTC and the FBI recommend. And never read out a code from a text message to anyone who calls you.
Can I get my money back after a SIM swap?
Call your bank as soon as you can – the sooner it knows, the better the chance of stopping payments still in progress. Then report it: in the US to IC3 at ic3.gov and to local police, elsewhere to the police or your national fraud reporting service. Whether the bank refunds you depends on the bank and your country's rules.
Sources
- FBI IC3 – Criminals Increasing SIM Swap Schemes to Steal Millions of Dollars from US Public (PSA I-020822-PSA, 8 February 2022)
- FTC – SIM Swap Scams: How to Protect Yourself (23 October 2019)
- FTC – What To Know About Identity Theft (September 2024)
- Czech Police – Cooperation between the police and a mobile operator helps catch criminals (2 July 2025, in Czech)
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