Available on Android 6.0(Marshmallow).
Long tap of the Home button on Android 6.0.
Setting for Android 6.0 :
This app settings > Set default assist app > Assist app > JB LockNow
JB LockNow is runs over Android 4.1(Jelly Bean).
You can now swipe up from the Navigation Bar to quickly turn off screen.
Google search with Google Now will start by swiping on the system bar,
You can replace the Google search, will be able to turn off the screen in the same operation.
Because now you can operate from the navigation bar, you can turn off the screen at any time.
* This app uses the BIND_DEVICE_ADMIN permission in order to provide the screen lock function.
* You will not be able to Google search, please use with confidence because you can disable from the configuration, remove the default apps.
* When using this application you will need to enable the device administrator (only lock the screen). Please enable dialog box is displayed when you start this app. Also, make the cancellation of this application from the configuration it is necessary to remove the device administrator when you uninstall this app.