The ever active developer community over at the XDA forums found a way to enable the double tap to wake function on Nexus 6 smartphones after the feature was removed by Google at the very last minute. However, this feature was limited to customers who have root access on the device which meant that those without it were left in the dark.
Well, we have some good news for you today as people with no root access can also make use of this feature now, thanks to XDA member qwerp_. However, your device will need to have the TWRP recovery installed and also have an unlocked bootloader for this feature to function. It’s rather strange to have a TWRP recovery and an unlocked bootloader but no root access. But it is good to know that there is an option for those users as well.
To gain this feature on your unrooted Nexus 6, all you have to do is flash the necessary file (link below) using the TWRP File Manager. You can find the instructions necessary to go ahead with the process in the link below.