Whenever you adjust the screen brightness or audio volume on a Mac you’ll see a small grey box overlay appear showing the current setting. This is sometimes known as a head-up display, or HUD.
Some people find it annoying, especially if they’re watching a movie because it can obscure the screen for several seconds before it disappears.
Here’s how to turn it off.
Turning off temporarily
To turn off the on-screen volume and brightness displays, open a Terminal window (you’ll find it in the Utilites folder of the Applications list) and paste in the following, which should be copied and pasted as a single line:
launchctl unload -F /System/Library/LaunchAgents/com.apple.BezelUI.plist
Restoring the overlay/HUD is easy: you’ll just need to log out and back in again, or simply restart your Mac.
Turning off permanently
To turn off the on-screen volume and brightness displays permanently, again open a Terminal window (as described above) and paste-in the following, which again should be copied and pasted as a single line:
launchctl unload -wF /System/Library/LaunchAgents/com.apple.BezelUI.plist
To turn them back on again, open the Terminal window and paste-in the following, which again should be copied and pasted as a single line, before logging out and back in again, or restarting your Mac,:
launchctl load -wF /System/Library/LaunchAgents/com.apple.BezelUI.plist