urxvt-ml-bell-command(1) - Linux man page
Name
bell-command - execute a command when the bell rings
Description
Runs the command specified by the "URxvt.bell-command" resource when a bell event occurs. For example, the following pops up a notification bubble with the text "Beep, Beep" using notify-send:
URxvt.bell-command: notify-send "Beep, Beep"