An IMEI (International Mobile Equipment Identity) is a unique 15-digit number permanently embedded in your iPhone that identifies it to carrier networks worldwide β like a passport number for your phone.
IMEI: The Full Meaning
IMEI stands for International Mobile Equipment Identity. Every mobile phone, tablet with cellular capability, and mobile broadband device manufactured since the late 1980s has been assigned a unique IMEI number.
The GSMA (Global System for Mobile Communications Association) β the international body governing mobile standards β oversees IMEI allocation. Manufacturers apply for blocks of IMEI numbers before producing devices, ensuring every unit gets a globally unique identifier.
What Does an IMEI Number Look Like?
An IMEI is exactly 15 digits long, always numeric, and looks like this:
It is sometimes displayed with spaces or dashes for readability, but the actual number has no separators β just 15 consecutive digits.
Breaking Down the 15 Digits
The IMEI is not a random number. It has a defined structure with each segment carrying specific meaning:
The Type Allocation Code (TAC)
The first 8 digits form the TAC. The first 2 digits identify the Reporting Body β the organisation that approved the device (e.g., 35 = British Approvals Board of Telecommunications, commonly used for Apple devices). The remaining 6 digits of the TAC identify the specific device model and variant.
This is why IMEI checkers can identify your device model just from the IMEI β the TAC is essentially a public model code. Apple's iPhone models each have a unique TAC assigned per model, storage tier, and region.
The Luhn Check Digit
The 15th digit is a mathematical checksum calculated from the first 14 digits using the Luhn algorithm (also used in credit card validation). Its purpose is error detection β if you mistype even one digit in your IMEI, the Luhn check will fail, immediately flagging the entry as invalid before any database lookup is attempted.
This is why our free IMEI Checker can tell you instantly if an IMEI is structurally invalid β without querying any database at all.
Starting from the rightmost digit and moving left, double every second digit. If doubling produces a number over 9, subtract 9. Add all the digits together. If the total is divisible by 10, the IMEI is structurally valid. This simple check catches ~90% of single-digit entry errors instantly.
How IMEI Is Used by Carriers
Every time your iPhone connects to a mobile network β to make a call, send an SMS, or use mobile data β it transmits its IMEI to the carrier's network alongside the SIM card's IMSI number. The carrier checks the IMEI against its Equipment Identity Register (EIR) database, which has three lists:
- White List β Approved devices that can connect normally
- Grey List β Devices under monitoring (e.g., suspected issues)
- Black List β Blocked devices (stolen, non-payment, fraud)
If your IMEI is on the Black List, the network refuses to allow the device to register β resulting in "No Service" even with a perfectly valid SIM card.
IMEI vs. Serial Number vs. MEID β What's the Difference?
| Identifier | Length | Used For | Who Uses It |
|---|---|---|---|
| IMEI | 15 digits | Cellular network identification | Carriers, law enforcement, GSMA |
| Serial Number | 10β12 chars | Device identification by Apple | Apple, repair shops, warranty |
| MEID | 14 hex digits | CDMA network identification (older) | Legacy US CDMA carriers (Sprint, Verizon old) |
| IMSI | 15 digits | Identifies the SIM card subscriber | Carriers (stored on SIM, not the phone) |
| MAC Address | 12 hex digits | Wi-Fi & Bluetooth identification | Network equipment, routers |
The IMEI and Serial Number are the two you'll encounter most often. The IMEI is used for carrier-related checks; the Serial Number is used for Apple warranty and service records.
IMEI on Dual-SIM iPhones
Starting with iPhone XS, XR (2018), Apple introduced Dual SIM support β a physical SIM slot plus an eSIM. Because each radio interface is independent, dual-SIM iPhones have two IMEIs:
- IMEI 1 β Assigned to the physical nano-SIM slot
- IMEI 2 β Assigned to the eSIM
Both are displayed when you dial *#06# and in Settings β General β About. For most checking purposes, IMEI 1 (the physical SIM) is the primary identifier used by carriers and checking services.
Can an IMEI Be Changed?
Technically, IMEI numbers are stored in firmware and can be overwritten with specialist tools. However:
- IMEI modification is illegal in most countries (a criminal offence in the UK, EU, US, and many others)
- It's used primarily by criminals to "clone" stolen devices with legitimate IMEIs
- Modern smartphones have hardware-level protections making modification difficult and detectable
- Carriers and law enforcement have tools to detect cloned IMEIs
If an IMEI check returns unexpected results for a device you own, the more likely explanation is a database error or a logic board replacement β not IMEI cloning.
Why Your IMEI Matters
Understanding your IMEI matters in these practical situations:
- π± Carrier unlock β Your carrier unlocks your phone by registering your IMEI as "unlocked" in their database
- π Theft protection β Reporting your IMEI as stolen blacklists it on carrier networks, deterring theft
- ποΈ Buying used β Checking the IMEI reveals if a device is stolen, locked, or misrepresented
- π Insurance claims β Insurers require the IMEI to process any lost/stolen claim
- π‘οΈ Warranty service β Apple cross-references IMEI and serial for service eligibility
- π International roaming β Network compatibility can be checked by IMEI
FAQ
IMEI stands for International Mobile Equipment Identity. It's a globally unique 15-digit identifier assigned to every mobile device at the factory, governed by the GSMA international standards body.
Legitimately, no β every device is assigned a unique IMEI. Duplicate IMEIs only appear on counterfeit devices or through illegal IMEI cloning. Cloned IMEIs cause network conflicts and are a criminal offence in most jurisdictions.
No. The IMEI is stored in the device's baseband chip hardware and is permanent. Factory resets, iOS updates, and software operations cannot change it. The only way an IMEI changes is through hardware replacement (logic board swap) or illegal modification.
No β these are completely different things. Your phone number is assigned by your carrier and is associated with your SIM card (IMSI), not your device. Your IMEI identifies the physical hardware. You can keep the same phone number with a different device, or use the same device with a different phone number.