What is an ESN and how can it go bad?

[Participant @shaharyar]

ESN is short for Electronic Serial Number, and it was first introduced by the FCC in the 1980s. It serves as a unique identification number of 32-bits which is used in mobile devices, and the number is usually found below the phone’s battery on a label. It is also programmed within the microchip of the phone itself.

The ESN codes are generally used in CDMA (Code Division Multiple Access) phones, which are the ‘radio type’ mobile devices, similar to the more widely acknowledged GSM (Global System for Mobiles). The purpose of the code is to authenticate the phone’s validity and to track them, and it is automatically sent to base stations when you make a call with your phone. If the phone is not considered valid, it’s ESN code will be banned by the network that the phone is on, rendering it useless. The ban is based on two main factors, which are if the phone is reported stolen, or if the owner has failed to keep up with their phone network billings.

The first 8 digits in the code represent the manufacturer code, and the rest of the 24 digits are the codes assigned to individual mobile devices. This was later altered, making the manufacturer code 14 digits and the rest of the 18 digits were for the mobile devices. The new method had a much smaller number of devices that could be possibly assigned, but it served as an alternative for new codes after the original amount was completed. As of now, the ESN authorization method is no longer in use in its original form, as all of the possible serial numbers have been assigned to devices. It was eventually revised into the MEID (mobile equipment identifier) system, which was assigned to devices to come after.

This means ESN, MEID, and IMEI are pretty much synonymous these days.

How the ESN can go bad for you as a consumer

A simple way to describe a banned ESN code is the term ‘Bad ESN’, which refers to the device being blacklisted by the carrier for any number of reasons. When a device has a bad ESN, it essentially becomes nothing more than paperweight. Unless the issue is resolved and the mobile device is reauthorized for use later. If the issue cannot be resolved, the device is forever tainted with a bad ESN.

The most common reason for an ESN may go “bad” is when the allowed amount of unpaid phone balance is exceeded. When this happens, the network that sold the phone eventually blacklists the device, which renders it useless as you can no longer use a network on the device.

The second reason for blacklisting a mobile device, although less common, is based on the device being reported stolen. Reporting a mobile device as stolen, and then the device getting blacklisted is a good thing for the original consumer, but it can be an issue when it comes to buying used devices, which is the next big factor.

There’s a huge risk factor when it comes to buying a used mobile device, there are many ways it can go wrong. For a non-ESN example, there’s the fact there could be a defect in the device that you could not have checked in time, such as a defective battery that has a lower life span than originally expected. When it comes to cases directly related to the ESN codes, the way it affects the consumer when buying a used device is that if they are buying from a person instead of a shop, especially if from an online source such as eBay or any other digital store, the device could have a blacklist for one of the reasons mentioned above. It could be a stolen or lost device, or it could have been one of the devices blacklisted after the bill had exceeded limits and was unpaid for too long.

If you purchase such a device, then your money is completely wasted, and someone who sold you such a device would make sure they are not reachable after the transaction is made, so there are no cases for returns. You have a device that cannot be assigned to a network and the entire purpose of having a cellular device is gone.

The right way to purchase a mobile device with ESN implemented is to make sure that in any case, you check the ESN before you make the purchase. Whether it’s a shop, a person, or someone you met through a digital store, ask the person for the unique ESN code on the device, which is almost always located below the battery of the phone on a label.

Once you obtain the ESN code before your purchase, you can either call the customer care of the company the phone belongs to and provide them with the code in order to check whether or not the device is clean. You could also try meeting the person you are about to purchase the phone from next to a store that the network on the phone belongs to, and check whether or not the phone’s ESN is clean.

Some companies no longer verify your ESN on the phone, so the store method is the only one valid in some cases, so double checking these details is important. Lastly, you could also note down the ESN code and check it on one of the websites dedicated to checking such codes, and eventually ensure that the device you are about to purchase. One example of such a site is CheckESNFree, and it is very straightforward. You simply select the carrier and enter your code, and the site lets you know whether or not the device is blacklisted.

After you have verified everything, you are safe to purchase the device and will avoid the risk of getting stuck with a phone with a bad ESN.

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