Having an unlocked bootloader really comes in handy in many situations such as flashing stock firmware (Stock ROM), installing TWRP and while rooting your Android device with Magisk. But it is important to know that there also downsides for having a bootloader unlocked device. Your device warranty is effectively null and void if your device has an unlocked bootloader. Sometimes, the device can also get blocked by the carrier due to security reasons.

Also, Google has an in-built security check known as the SafetyNet which considers a device with unlocked bootloader as a security risk. This will in-turn disable certain services such as Google Pay and other banking applications. That is the reason why you might need to relock the bootloader of your Android device.

Fortunately, the process to relock the bootloader of an Android device is relatively easy and will solve all these issues for you.

1. Your device data will be completely wiped out once your relock the bootloader of your device. We strongly recommend you to take a full backup of your Android device before proceeding.
2. Please note that the fastboot command to relock bootloader is not the same for all Android devices. And that is why we have compiled a list of most commonly used Fastboot commands to relock the bootloader. You can try the fastboot commands only by one.

How to Relock Bootloader on Android

1. Setup ADB and Fastboot on your computer.
2. Go to the folder where you have the ADB and Fastboot tools. Open a command prompt from inside this folder. To do this: Hold down Shift Key and Right-click on the empty space inside the folder and then select ‘Open command window here‘ or ‘Open PowerShell window here‘.
3. Run the following command to boot your device into bootloader mode:

   adb reboot bootloader

4. Next, use just one of the following commands to relock the bootloader. You don’t need to use all the commands given below. If one of the commands work, you can skip to the next step.

   fastboot oem lock

   fastboot flashing lock

   fastboot oem relock

5. Once the bootloader is locked, run the below command to reboot your device:

   fastboot reboot

I hope this helped you relock the bootloader of your device. Did the commands mentioned in this guide work out for you? Did we miss to add any command for your device/manufacturer? Do let us know in the comments.