Older iMacs can be used as external displays for other Macs. Target Display Mode works seamless, but if you want to turn your iMac off after a day of work and keep your other Mac on, you’ll need to click CMD+F2 to switch again or unplug/plug the cable on the next day.

I took a few minutes and I wrote a code in C++ that did the CMD+F2. It worked for a while. Then, I figured that “while” was while my Apple Keyboard was connected to the iMac.

Luckily, I found a blog post on the internet about reverse engineering the thing, so it explains how Apple does to switch display modes (Source: https://floe.butterbrot.org/matrix/hacking/tdm/). Finally, my job was to find a way to write bytes to SMC.

It was mentioned that SMCKit (https://beltex.github.io/SMCKit/) was used to tests, so I cloned the repo and installed on my computer. The CLI is focused on temperature, but the kit had what I needed, so I wrote another option to the CLI to write the bytes where I needed. And boom! It worked!

Lastly, I don’t want to keep any input device plugged in my iMac, so I created a plist and added to LaunchAgents saying that it should be run in “LoginWindow”. I restarted my iMac and TDM was set automatically. Now, I have a “Cinema Display” running on my MacBook Pro.