tmux pane-activity indicator behavior with concurrent pane activity

Pane-Activity Trigger and Reset Behavior

In tmux versions 3.1 through 3.3, the pane-activity flag is triggered exclusively by new output written to the pane's terminal. Key presses that do not result in output (such as Ctrl+C or arrow keys in a silent shell) do not trigger the activity flag. Conversely, if a key press causes the shell to echo a character or print a new line, that resulting output triggers the flag.

Viewing a pane by making it the active pane does not automatically clear the pane-activity flag. The flag persists until the pane produces new output while it is already being viewed, or until the monitoring state is manually toggled.

Concurrent Activity and Visual Indicators

When multiple panes generate activity simultaneously, tmux does not prioritize one over another. Each pane maintains its own activity flag. The visual-activity indicator in the status line will display markers for every pane that has the flag set, typically ordered by the pane index.

Operational Nuances

While the internal flag is set based on output, the visual representation of that flag can be suppressed under specific conditions:

• Active Pane: The visual indicator is often suppressed for the pane that currently has focus, as the user is already observing the activity.
• Mouse Mode: Enabling mouse mode may interfere with or suppress certain visual-activity notifications depending on the specific version and configuration.

Verification Steps

To verify this behavior in your current environment, use the following scoped commands:

# Enable activity monitoring and visual indicators
tmux set-option -g monitor-activity on
tmux set-option -g visual-activity on

1. Split into two panes. In Pane A, run echo "test"; the indicator should appear.
2. In Pane B, press Ctrl+C; no indicator should appear.
3. Switch focus to Pane B; observe that Pane A's indicator remains visible.
4. To manually clear flags, toggle the monitor setting: tmux set-option monitor-activity off && tmux set-option monitor-activity on.

Diagnostic Detail: If you are not seeing indicators for multiple panes, please specify if you are using a custom status-left/status-right string that might be overwriting the default activity display.