Can external monitors follow my MacBook’s automatic brightness?

Yes, when BetterDisplay can detect the built-in display's hardware brightness changes and the external monitors have working brightness controllers. Configure group synchronization to follow those changes, including changes made automatically by macOS.

1. Enable automatic brightness for the built-in display in macOS and keep its Apple hardware brightness control enabled in BetterDisplay.
2. Include the built-in display and external monitors in an active group under Settings > Groups.
3. Open that group's Synchronization Settings, enable Enable synchronization for this display group, and add or enable Brightness synchronization.
4. Allow the built-in display to be a synchronization source and the external monitors to receive its changes. Enable Synchronize changes triggered externally for the Brightness entry.

Basic Brightness synchronization in the Default Group is available without Pro. Custom groups and advanced synchronization options can require Pro. The external monitors need not have their own ambient light sensors: this setup follows the built-in display's brightness, rather than using the sensor's lux reading directly as the synchronization source.

To check the setup, change the built-in display's brightness in macOS Control Center while watching BetterDisplay's brightness slider. If BetterDisplay reflects the change but the external monitors do not respond, check that the group is active and both the group and Brightness entry have synchronization enabled. Then check that the built-in display can send changes, the external monitors can receive them, and their own brightness sliders work. If BetterDisplay does not reflect the change, check the built-in display's enabled hardware controller first.

Delta syncing preserves differences between starting brightness levels by following the amount of change. Turn it off to follow absolute values instead. Matching percentages does not guarantee equal perceived brightness. The displays' ranges and capabilities still matter.

See Synchronization Settings for source filters, external changes and range matching. You do not need to reset all app settings as the first troubleshooting step.

The Touch Bar’s brightness slider changes the built-in display through macOS. Brightness control using native brightness keys does not intercept it as a keyboard brightness event. The group synchronization above can propagate the resulting built-in brightness change to external monitors. This follows a change after it happens rather than remapping the Touch Bar slider itself.

For a step-by-step setup with the built-in display as the source and external monitors as receivers, see Make external monitors follow your MacBook’s automatic brightness.