Unlocking your bootloader allows you to put custom software onto your device. Many developers have created custom ROMs and have had to hack their way into the ZenFone 2 to make this available to powerusers in the community.
Now, unlocking the bootloader is as easy as downloading the utility, installing it, and running it.
Proceed with caution and read below notice before attempting
Download the utility HERE
From the ASUS Support site: Unlock Device App: Unlock bootloader
Notice: 1. Update your software image to V126.96.36.199 or latest version 2. Before you download, install, and use the Unlock Device App you acknowledge and assume complete risk to the quality and performance of this App, including but not limited to the following: once you activate the App you will not be able to recover your ASUS product (“Original Product”) back to original locked conditions; the Original Product with the activated App will not be deemed the Original Product; the Revised Product will no longer be covered under the warranty of the Original Product; the software of Revised Product will no longer be deemed the software of the Original Product and can no longer receive ASUS software updates; your purchased digital content may also be affected.
You also acknowledge ASUS does not guarantee service satisfaction to any Revised Product, including events involving paid service requested by you to be performed to the Revised Product. Furthermore, such repaired Revised Product will not be covered under the warranty of the Original Product; the software of the repaired Revised Product will not be deemed the software of the Original Product and will not receive ASUS software updates. It is strongly advised that you avoid activating this App unless you fully understand and accept the risks that may arise.