urxvt-bell-command (1) - Linux Manuals
urxvt-bell-command: execute a command when the bell rings
bell-command - execute a command when the bell rings
DESCRIPTIONRuns 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"