Remapping hardware buttons on Android

I own a Nexus 5 (several, actually) for a while now, and every few months the power button starts to fail (due to usage)? Sometimes it gives off a signal by itself, like it's stuck. And the screen starts to flicker.

Replacing the #Nexus5 power button. #electronics #DIY.

A video posted by Jean Caffou (@jeancaffou) on Feb 13, 2016 at 3:01am PST

But recently the power button just died. For two days I had to press it really hard for it to make contact, but now, nothing works. I'm not a hardware guy myself, so to replace the button physically I need to visit my geeky electronics hacker friend. And it sucks begging people for help. So to workaround it for as long as possible let's try software solutions.
Apps - they work without root, sure. But all of the ones I tested were kind of buggy. One worked on proximity sensor, the other one tried to remap the volume button. But the problem with all of them was they were sending the WAKE command to turn the screen on. And I sometimes had no way to turn the screen off. Except for, you know, using another app. The WAKE command was causing a weird bug when I was ending a call.
When calling, the system turns the screen off and on based on proximity (if you have your phone on your face), so sometimes the device didn't go to sleep, EVER, but the screen was off. So WAKE command did nothing, because the phone thinks that it's still on. So I was stuck.
To get out of this loop, I powered up the adb and sent the POWER command instead of WAKE.

adb shell input keyevent KEYCODE_POWER

The first time I sent this, nothing happened, but internally, the phone went to sleep. The second time I sent it, the phone powered back on. So now I know the problem. And do I really need an app to remap the power buttons?

Turns out, I don't.

There is a system file (unfortunately you need root to edit it) which defines all of the keyboard layout including hardware buttons. It is located in:

/system/usr/keylayout/

Inside of this folder there are a bunch of .kl files - you need to find the right one and open it up.
There you will find the definitions such as:

key 114 VOLUME_DOWN
key 115 VOLUME_UP
key 116 POWER

Just change the "VOLUME_" ones to POWER.

Reboot to apply changes.

I'm not sure if I'll be able to power on the device if the battery dies, but it works for locking/unlocking.

Because this file is only read on boot, it might work if the device is plugged in a charger so that it boots and reads the definitions.