Xtrlock : Minimal lock program
Sometimes you want to lock your screen but still want to view what your machine is doing.
xtrlock is simple and just does that.
sudo apt-get install xtrlock
Type in a terminal ‘xtrlock’ and a little icon replaces your mouse cursor. To unlock just type your password.
You can also add a shortcut in a menu or whatever you like.
If you still like to blank your monitor use: xtrlock -b