In the end I used https://www.emacswiki.org/emacs/AlarmBell and added some code to overwrite-mode-hook
(defun double-flash-mode-line () (let ((flash-sec (/ 1.0 20))) (invert-face 'mode-line) (run-with-timer flash-sec nil #'invert-face 'mode-line) (run-with-timer (* 2 flash-sec) nil #'invert-face 'mode-line) (run-with-timer (* 3 flash-sec) nil #'invert-face 'mode-line))) (add-hook 'overwrite-mode-hook #'(lambda () (double-flash-mode-line)))