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    IMEI number vs IMSI: what you need to know about them

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    Pau Monfort
    @paumonfort

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    Most of us don't pay attention to details like IMEI and IMSI numbers. When we need them, we don't know what they are or how to find them. Should we at least know how they differ from each other and where they are? These are important questions for your privacy and security. Many of us have heard of the IMEI number as it is very useful for finding lost smartphones. But what about IMSI numbers and what their role is.




    1. What is the IMEI number

    IMEI stands for International Mobile Equipment Identity. Each mobile phone (and new mobile hotspot dongle) is assigned a unique IMEI number, which is printed on the inside, usually behind the battery pack. They are 15 digits long. Phone manufacturers assign unique IMEI numbers to each phone and these numbers remain the same once registered for the rest of their life. So even if you travel to other countries, telecom operators can identify the country of origin of the sale and registration of the phone.

    The GSM (Global System for Mobile) association uses IMEI numbers to store them in a global mobile database which is also central to all network operators, phone manufacturers and other qualified parties in the industry. The number is useful for identifying things like subscription usage (voice calls, Internet) and determining if there are any issues with the quality of services.

    The IMEI number is just as important as the serial number on other products. Hence IMEI numbers are used to identify the authenticity of a phone registered via a SIM card. IMEI numbers only prove the authenticity of the phone and do not establish any direct relationship with the buyer.




    For example, you may have purchased a new phone to give to your parents or spouse. While you may be the buyer (technically), the end user of the phone can be different.

    Telecom companies often use in exceptional circumstances such as detecting blocked or invalid phones on the network used for suspicious activity. In the case of CDMA phones, manufacturers use a different terminology called the Mobile Equipment Identifier (MEID) or Electronic Serial Number (ESN).

    The IMEI number is the first thing a telecom operator's customer care executive asks if your phone is lost or stolen.


    2. What is the IMSI number

    IMSI stands for International Mobile Subscriber Identity. The telecommunications company assigns a unique number assigned to the SIM card it issues to its subscribers. IMSI numbers are 15 digits long (not always though) and can be used to find the subscriber's country and mobile network, among other SIM-related details. It is tied to the SIM card rather than the phone itself.

    It is worth noting that to protect subscriber privacy, telecom operators instead use another number called TMSI (Temporary Mobile Subscriber Identity) while providing services to the SIM owner. The telecommunications company uses the TMSI to communicate with its subscriber. They are also shorter and much easier to pass on.

    3. How to find IMEI AND IMSI numbers

    If your phone has a removable battery, you can find the IMEI number printed under the battery. You can also find it printed on the original box, surely you threw the box away a long time ago, right? Alternatively, you can dial the code * # 06 # in the phone dialing app to see a pop-up with your IMEI number. It is usually 15 digits long and is programmed into the phone.




    If you are shown two IMEI numbers this is because you are using a dual SIM phone and each of them must be registered with the operator. Usually, only the last few digits are different in these cases. It helps the operator to identify and track these phones with IMSI numbers.

    Several smartphones have started showing the IMEI number in the About section in Settings. Check if your phone also shows the IMEI number.

    As an end user, you do not need the IMSI number attached to the SIM. Some cell phone manufacturers list the IMSI number in Settings in the Information or Phone Information section, but it is rare.

    Final report: some apps also claim to help find it, but we don't recommend them. It is not worth it and there are chances that the information can be used to track the user in question. If you need it, call your telecom operator.

    4. When to use IMEI AND IMSI numbers

    Since IMEI numbers are unique and cannot be changed easily, they are very useful for tracking and recovering lost or stolen phones. It is used to identify the mobile as all IMEI numbers are stored in a global register called the Equipment Identification Register (EIR). 

    Your telecom provider has the power to blacklist or block your phone. When a phone is blacklisted on all networks, no SIM will ever work on it. This means that the phone is practically useless. I think the WiFi might still work.


    Hackers use aftermarket tools to make a quick profit by changing the IMEI number. This is called unblocking, which is a criminal offense in many countries. These hackers use tools to assign a new IMEI number (also known as spoofing) to the phone so that it is unlocked and reused with a different SIM card. You can face the legal consequences of spoofing your cellphone IMEI number if it is used for nefarious activities.


    On the other hand, when you transfer your SIM card from one phone to another, the IMSI number carries over to the new phone with the SIM. The IMEI number remains with the phone as it is connected to the phone. Telecom operators use the IMSI number to identify the customer and all the services they have subscribed to. This includes calling, messaging, Internet and other services offered by the company.

    5. Security Issues

    It is important to protect your IMEI and IMSI from the prying eyes of malicious apps and trackers. Hackers can use the IMEI number to track and locate your movements. Heck, they can even fake it to use financial apps after they steal your data.

    On a related note, if you find a phone without an IMEI number then it is an invalid or counterfeit phone. You shouldn't buy it, no matter how attractive the price is. How do you know your IMEI number is valid? Well, you can match the one shown in the software interface with the one printed on the back and the packing box. Another way to check this is to use the LUHN formula.

    Likewise, IMSI numbers can be used by hackers to track users, intercept calls, messages, and hijack mobile data. This is because the IMSI number is tied to the SIM card and is used directly to provide relevant services to the subscriber.

    Hackers can create a fake access point to capture the data associated with the IMSI number before forwarding it to the nearest cell phone repeater and vice versa. A lot of Hollywood movies show that trick for tracing calls and all. However, the actual use of such a technique is an extremely complicated process. Not impossible, though.

    Since the IMSI number is tied to the SIM and used when communicating with cell towers, it can also be used to track the user's movements. In that case, the location of the cell towers is used to triangulate the location.

    That said, the IMEI and IMSI can be pulled from the mobile apps to create a personally identifiable profile based on the usage pattern.

    For example, based on your browsing activities, different companies may show you specifically targeted ads. And you may be wondering, how did that company know you wanted to buy a new jacket? Well, it could be any app that you have blindly allowed to access any information on your phone.

    Conclusion

    IMEI is tied to the phone and is used to identify the phone. The IMSI is linked to the SIM card and is used to identify the subscriber and the services assigned to him. IMSI moves from phone to phone with the SIM, but IMEI stays with the handset. As an end user, you will find IMEI useful for blocking lost or stolen phones.

    This is the gist. It's a good idea to keep your IMEI number somewhere safe so that when the time comes, you can use it. If the IMEI number is visible in the Information section in the Settings, take a screenshot and save the image to the cloud.

    Further Reading:

    • How to find IMEI number on any Huawei / Honor device
    • How to change or reset IMEI without root?
    • How to block a stolen phone via IMEI
    • How to check if a Xiaomi product is original
    • How to unlock iPhone SE 2020 and use it with another carrier
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