Disabling laptop monitor when external HDMI monitor is plugged in

Using xrandr

• Open a terminal window.
• type xrandr. It will list all video ports. 2 will have some data below them 1920x1200 etc. One is tv the other is laptop monitor.
• Assuming the laptop monitor is called LVDS1 then type xrandr --output LVDS1 --off

There is also a graphical tool to do it, but I know not of how to do this using the ubuntu unity desktop. (If you are running kde, gnome or other then do tell.)