Trigger action on external monitor plug/unplug I'd like to trigger an action (launch an app, execute a script…) when I plug or unplug an external monitor on my MacBookPro with macOS 10.13.5.

Is there any native way or third party app to do that?
There is ControlPlane, but I didn't have much luck with it on El Captain.

Other option is running a never-ending AppleScript which calls your script on change of number of monitors. See this answer.