A locked bootloader generally means that you would not be able to install customized software into your Android device. Locked bootloaders are the bane of existence for many of the users who exercise their rights of making changes to the software, for example, in Sony Xperia devices. The ASUS ZenFone 2 was once upon a time a part of that list but not anymore. “ravian29”, an XDA forum member has printed a way to unlock the bootloader, and the instructions look uncomplicated and easy to understand. One must always remember that this process not quite always begins by obtaining root access, and that does not deprive any kind of warranty from the manufacturer. Generally, the process is simple where users with their smartphones connected make use of the ADB installed on their computers and input a few commands. Check out the source link below for full instructions. In his post, the thread starter mentioned that there will not be any data loss if instructions are followed. However, he also suggests to back up data in the event something that is not expected happens. So, before you try this on your ASUS ZenFone 2 make sure that your data is secure. How to unlock bootloader:

  1. Update to 2.19.40 2. root it 3. make sure adb is insatlled and working 4. enter the following commands in cmd adb shell (press enter) su (press enter) getprop ro.isn > /factory/asuskey ( press enter) reboot bootloader ( press enter ) Phone will restart in bootloader and after updating itself phone will restart again and ASUS splash screen will be white ( locked bootloader has black screen, you will see difference by yourself)
  2. download black splash screen from here https://mega.co.nz/#!IlMGiZ7I!kepXRF…4UufAJT6YEDU3k
  3. navigate to adb folder open cmd and type the following commands adb reboot bootloader (press enter) fastboot devices (press enter) see if device is listed, write following fastboot flash splashscreen splashscreen.img (press enter) restart your phone and now black splash screen is back. Congrats your bootloader is now unlocked. If you follow my steps there would not be any data loss from internal memory and sd card, but i will advice to take a backup in case if you are out of luck Kindly remember the unlocking bootloader voids your warranty and if you are not comfortable with handling the system commands you may end up bricking your Zenfone. Please visit the XDA Forum link for more information. SOURCE: XDA