Anyone know how to turn off the Macbook pro display with the lid open while using external monitors on Mac OS X 10.10 Yosemite? (I am aware that you can just close the lid, but I want to keep this open for air flow purposes and turning down the brightness is not the same as turning the display off as the GPU still sends a signal to the display thus uses more battery and creates more heat.) On Mavericks this worked just fine as mentioned in the link: http://gizmodo.com/5938452/a-trick-to-make-using-an-external-monitor-with-your-macbook-way-better TL;DR Here is a terminal command thats fairly simple that will allow you to keep the lid open for adequate cooling but while using the external display only. I've been using this method with my Thunderbolt display and MacBook Air since the beta of Mountain Lion came out and it works perfect. Has all the same characteristics of good old clamshell mode. Be sure to keep this written down someplace in the off chance you need to re-install, do a PRAM reset, or just want to undo it. To execute in Terminal: sudo nvram boot-args="iog=0x0" To undo in Terminal: sudo nvram -d boot-args Once you type it into terminal I believe you need to enter your password. I then restart my machine. Now the TRICK is to either restart your machine with the lid already closed (hit restart then slam the lid!) OR turn the machine on for the first time (then quickly slam the lid!) once you are past the login screen you can open the lid.