Un-greys your volume keys.

The grey slider problem.

Run two Studio Displays — or any monitors-plus-headphones combo — through a Multi-Output Device, and macOS greys out your volume keys and the menu-bar slider. The keys do nothing. The slider is dead.

Halo fixes it.

A tiny menu-bar app that intercepts F11 / F12 / mute and writes the volume to each speaker of the aggregate directly — so everything moves together.

• A proper volume HUD — replaces the one Apple broke on macOS Sequoia
• 32 fine volume steps instead of 16
• Scroll-wheel volume on the menu-bar icon
• One-click Create Halo Speakers for Studio Displays
• Levels remembered across reboots