Define different screen resolution when external monitor is plugged in on MBP retina w/ OSX 10.9 I have a MBP retina with OSX 10.9 on it and I'm trying to automatically change my laptop screen resolution when an external monitor is attached or detached. This question is the same but for a different version of OSX and doesn't work with my version.

For example, when I attach an external monitor, I want the laptop screen to display at a lower resolution, then when the external screen is removed I want the laptop screen to display at the highest resolution again.

Is there an easy way to do with, or can someone give me step by step instructions?
There is an app called SwitchResX that, I believe, will allow you to predefine resolutions based on which display you are using. It costs about $20 but it's shareware, so you can try before you buy.