Otherwise your device may misbehave.This will never Possible Without XDA developer ravian29. Who make this possible to unlock bootloader without contacting Asus.
#What is use of unlocking bootloader ?
well You will be happy to know that after unlocking bootloader you can flash Stock android or CM custom Roms and many other Roms when they build .Hope so it will build Soon.Lets start the tutorial.
#Read the below line loudly first.
DISCLAIMER: Neither I or anyone else is responsible for anything that
can happen to your device when using this.
Your phone = Your
So lets start the Step by step Guide to Unlock Boot loader of Asus Zenfone 2
#How to unlock Bootloader of Asus Zenfone 2 without ASUS
1.Firstly you need to Update your Asus Zenfone 2 To 2.19.40.
3. Download Fastboot : https://userscloud.com/21c02xsuiokm and extract it.
4. Now open the extract the folder and Hold down Shift and right-click anywhere on your screen and select Open
command window here option.
5.It will launch a Command Prompt Window for you to
issue commands to your device.
6.Now try the following commands One by one in sequence to unlock bootloader
adb shell (pressed enter)su (pressed enter)
getprop ro.isn > /factory/asuskey ( pressed enter)
reboot bootloader ( pressed enter )
7.Now your Phone will restart into Recovery mode and start updating after updating it will restart ASUS splash screen will be white ( locked bootloader has black screen, you will see difference yourself).
8.Now download The black splash screen from here. And place it in the adb folder that you extracted above.
9.To flash this Splash screen Tye the following commands in The CMD that you opened above.
adb reboot bootloader (pressed enter)
fastboot devices (pressed enter)
see if device is listed, IF yes the Type the following
fastboot flash splashscreen splashscreen.img (pressed enter)
10.Now restart your phone and Now black splash screen is back. Congrats your bootloader is now unlocked.
If you face any problem in unlocking to Bootloader you can ask below.
source:unlock bootloader of zenfone 2 XDA