Try this please to add bell-action other for bell in not current window.
I don't think we want an option to alter the visual bell message, I
don't think bells are used that much.
You could probably script changing the title by looking at
window_bell_flag (or tmux showmsgs).
Index: options-table
Hello,
I like tmux, but there is one feature from GNU screen, which is missing
for me. In screen I use belling, but only if they appear in windows in
background. I don't need bell in current active window, but need to know,
if something happens in non-visible windows. How can I do this in tmux?
