Margen
Dial *#06# on your phone’s keypad and look at the 15 numbers that come up. That is the IMEI, the handset’s own number, and it is exactly what you will be asked for on the day you no longer have the phone to dial it on. It is not your phone number, it is not stored on the SIM card, and it does not change if someone puts a different one in.
The difference matters and everybody mixes it up. Your number lives in the SIM: you throw it away, you ask for another and you are still you. The IMEI lives inside the device, and it is the only way a carrier can say that this thing does not connect.
On the day of the theft the order matters, and the order INCIBE recommends, Spain’s public cybersecurity institute, is not the obvious one. The first thing is not to ring anybody: open Find My Device if you are on Android, or Find My iPhone if you are on an iPhone, and locate the handset and lock it from a distance. The second is to ask your carrier to cancel the SIM card, and that comes afterwards and not before for a reason INCIBE itself flags: blocking the SIM can leave you without location services. The third is to report the theft to the police, giving them the IMEI. And the fourth is to ask the carrier to block the handset, which takes both the IMEI and the police report.
So you need the IMEI twice, to file the report and to get the handset blocked. And after the theft there is no keypad left to dial *#06# on.
Now the small print, which is the part I care about. A blocked IMEI will not register with any carrier’s SIM, but what gets blocked is the line, and your photos, your email and your banking app are still sitting where they were. INCIBE puts the remote wipe right after locking it, with a condition worth reading in full: do it if you no longer expect to get the handset back. Because once you wipe it you also lose the way of finding it. Me, with my banking app in there, I wipe it and write the phone off.
Two more warnings I can see coming. The phone’s box also carries the IMEI on a barcode sticker, but the box is at your parents’ house and the theft happens in the street. And some carriers want the police report before they will block anything, so do not count on sorting it out in a three-minute call from the station.
Do it now, it takes 20 seconds. Dial *#06#, take a screenshot and email that picture to yourself. The only thing that matters is that it ends up stored somewhere that is not the phone.