The above commands will blank your monitors, but they will not turn them off completely. Many users wish to listen to music on their computers/laptops and conserve power. Or just get up for a coffee and not have someone mess with your workstation.
To turn off the monitors completely, create the following script in your editor of choice.
Code:
!/usr/bin/env bash
xset s blank ; sleep 1 ; xset s activate
cinnamon-screensaver-command -l
Save, name sleeplock.sh or whatever you choose.
You will need to give the script permission to run as an executable and bind it to a key. I use Cntrl + M, you can use whichever you wish.
Notes:
Modify cinnamon-screensaver-command -l to gnome-screensaver-command -l for gnome desktop.
mate-screensaver-command -l for MATE desktop, xfce-screensaver-command -l for XFCE desktop.