Detect Displays on macOS

Sometimes when I use an external display with my MacBook Pro in clamshell mode, nothing shows up — I just get a black screen. And when this happens, forcing macOS to “Detect Displays” can help.

To trigger “Detect Displays” on macOS, just hit Command+F2 (brightness up).

You can also do this using the trackpad:

Navigate to System Preferences > Displays

Hold down the Option key to reveal the Detect Displays button

Click Detect Displays

This works in macOS Mojave, and others have reported it works with previous versions of macOS.