======= iMacMonitor - Enter Target Mode programatically

• License: MIT license (bogner.sh)
• Original site: http://bogner.sh/2013/07/os-x-how-to-use-an-imac-as-monitor/#comment-50925
• Repo: Placed on github.com/lsd for convenience and for my own edits
• Desc: Set to run on login with auto-login account to turn iMac into a permanent external display without needing a keyboard

This is for Xcode5 and OS X 10.9. For older releases, the pre-10.9 directory

This is originally from http://bogner.sh/2013/07/os-x-how-to-use-an-imac-as-monitor/#comment-50925 All original links preserved

How to use an iMac as Monitor

Think about the following rather unusual scenario: You own a current generation MacBook Air and a new iMac that you don't use. This blog post will show you how you can use the iMac as a pure monitor without any manual intervention.

Introduction

The current generation iMacs (21" and 27") can be used as a Thunderbolt display using Target Display Mode. To enabled this mode you have to boot both Macs and connect them using a Thunderbolt cable. After that you have to press [Command]+[F2] on the keyboard of the "display" iMac. Although this feature is great for rare usage – it’s not very comfortable if you want to use the iMac as a permanent secondary display.

iMacMonitor

To solve this problem I created iMacMonitor. It’s a small application running on the “display” iMac that monitors the Thunderbolt bus and automatically switches to Target Display Mode if necessary. Thereby one only has to connect the main computer to the Thunderbolt cable and a few seconds later the iMac can be used as a secondary monitor. This works because Mac’s wake from standby if a Thunderbolt device is connected. As soon as the main computer is disconnected the display will sleep again. Be aware that you should not shutdown the “display” computer as it won’t switch to Target Display Mode anymore.

Setup

1. First you have to download iMacMonitor.app on the "display" iMac and set it as Login Item.
2. Then make sure that a user is automatically logged in (see this
   link).
3. Restart
4. Voilà

Now you can connect a Thunderbolt enabled Mac and the “display” iMac
will switch to Target Display Mode automatically.

Sourcecode

As I have written this application for fun you can also download the
Xcode project.
It’s released under the MIT licence.

Update: Here’s the Xcode 5 Project for 10.9