We’ve grown addicted to the double tap to wake feature that became quite popular on phones in recent years, but not every phone has the feature. This was true for the Nexus 6P… until it was discovered that code for the feature does actually lay dormant in the device’s kernel.
There’s one problem with this, though — the feature won’t stick on a device reboot. That’s a bit sucky, but the developer is working on an update to his custom kernel that’ll bring the feature permanently. In the meantime, if you want to use it be sure to enter the line above into your terminal emulator, and enjoy. If you reboot your phone, simply repeat that step (including the whole enjoy bit, too!).