How to Lock the Bootloader on Nokia Android phones

Nokia phone users who have unlocked their bootloader can re-lock it at any point. Re-locking will remove the boring 5-second warning which shows before every boot. Your Nokia device will also pass the Android SafetyNet, allowing full access to Android Pay, NetFlix, and other services.

Also, if you have only unlocked your bootloader to flash the stock ROM, then it is a good idea to lock it after everything works fine.

Before locking the bootloader on your Nokia phone, ensure the following:

You have made no modification on the system partition(s) and you are running stock ROM and stock recovery.
You are on the same operating system as officially sold with the phone. For example, do not lock the Nokia 7 plus if Android P beta is installed.
If you have made any changes to system, then flash the stock ROM.

Warning: Locking the bootloader will wipe all data stored on your device. So, backup important data before proceeding.

Steps to lock the bootloader

Applies to: Nokia 1, Nokia 1 Plus, Nokia 2, Nokia 2.1, Nokia 2.2, Nokia 2.3, Nokia 3, Nokia 3.1, Nokia 3.1 Plus, Nokia 3.1 Plus C, Nokia 4.2, Nokia 5, Nokia 5.1, Nokia 5.1 Plus, Nokia Nokia 6, Nokia 6.1, Nokia X6 (Nokia 6.1 plus), Nokia 6.2, Nokia 7, Nokia 7 Plus, Nokia 7.1, Nokia 7.2, Nokia 8, Nokia 8 Sirocco, Nokia 8.1, Nokia 9 PureView, Nokia X71., Nokia 6.2, Nokia 7.2 and others.

Reboot your Nokia phone to download mode.
Connect to the PC using the USB cable.
Check that your phone gets recognized by Fastboot by running:
```
fastboot devices
```
Run the following command to lock the bootloader.
```
fastboot flashing lock
```
If the command is not recognized, use:
```
fastboot oem lock-go
```
Confirm the bootloader lock on the phone. It will erase all existing data from the device.
If you have also unlocked critical, then bring the phone into fastboot mode again and run the following command. After that confirm the lock on your phone after running.
```
fastboot flashing lock_critical
```