What is a Bad ESN on My Phone, and How Do I Fix It?

An Electronic Serial Number, or ESN, is a unique 32-bit identification number stored in wireless phones' microchips. Created by the U.S. Federal Commission, ESN’s main goal is to identify cellular devices uniquely. Think about it as your phone’s digital fingerprint. Traceability is essential because it aids in quality control and results in more transparency across manufacturing and post-purchase stages.

How Does ESN Work? The electronic serial number is embedded in the wireless phone’s microchip. Each time you’re making a call, the ESN is automatically transmitted to a base station. The mobile operator uses this essential step to authenticate the number, check the validity of each connection, and prevent fraud.

How to Find Your ESN? Luckily, there are several ways to obtain the serial number:

• Check the Settings. Whether you’re an iOS, Android, or Windows user, go to Settings and look for the ESN in the About Device section.
• Look on the Phone. The ESN is located on the back of the device, like under or below the battery or near the SIM tray.
• Inspect the Packaging. If you still have the original packaging of the device, the ESN code will be indicated near the UPC barcode.
• Find It Online. You can often find the number on your provider’s platform.

What Do the Numbers Mean? Originally, the first 8 digits were used to represent the manufacturer code, while 24 others were dedicated to creating unique codes that manufacturers assigned to their products. The system came with a handicap: the first 8 digits created a unique code for only up to 256 manufacturers, while the latter symbols allowed manufacturers to assign a limited amount of codes. This limitation paved the way for a new system: in 2006, the manufacturers exhausted all the possible unique combinations and transitioned to the new MEID standard.

ESN vs. IMEI vs. MEID: Is There a Difference? The terms are not interchangeable, although they’re used to identify a device uniquely.

• IMEI, or International Mobile Equipment Identity, is found in devices reliant on GSM technology that uses SIM cards for authentication.
• MEID, or Mobile Equipment Identifier, is typically found on older devices tied to CDMA technology that uses the device’s unique identifiers.
• ESN was mostly used by CDMA carriers before the unique numbers were exhausted, and it started getting replaced by MEID.

The mobile phone can support either CDMA or GSM but not both.

Basics aside, let’s get to the main issue: what is bad ESN, and how does it affect you? A bad ESN refers to a device flagged as stolen, lost, or tied to an account with unpaid bills. More rarely, it can occur due to a technical glitch within the system or issues of administrative origin. Whatever the reason, the device can be activated neither on the original carrier’s network nor by most U.S. carriers.

Before purchasing the used phone, ensure it doesn’t have a bad ESN. Luckily, you don’t have to be a tech wiz to check it yourself. Here’s what you need to do:

• Make sure the device is compatible with your network. You can either activate the current SIM card or swap it for a new one.
• Attempt to make calls or send messages. If you can’t do it, it’s one of the best indicators that there could be an issue with the ESN.
• Call customer service. After you provide the model, make, and IMEI number, the service provider will be able to tell you more about the issue and how to fix it.
• Reset the device. Customer service may recommend you restart the device or perform a factory reset (remember that it will erase your personal data).

Although certain software kits and cleaning services promise simple and fast solutions to the problem, this approach can often result in even more damage to the device, especially if things go really wrong.