Here is a `git diff -p org-timer.el' of the changes that I am proposing.
diff --git a/lisp/org-timer.el b/lisp/org-timer.el
index 2351c4c..cb0ce45 100644
--- a/lisp/org-timer.el
+++ b/lisp/org-timer.el
@@ -93,6 +93,25 @@ nil current timer is not displayed"
(defvar org-timer-cancel-hook nil
"Hook run before countdown timer is canceled.")
+(defvar org-timer-message nil
+ "Message displayed after countdown timer reaches zero. If
+ org-timer-message is not a string, then the default message
+ will be displayed.")
+
+(defcustom org-timer-clock-sound t
+ "Sound to play after the countdown timer reaches zero.
+Possible values are:
+
+nil No sound played
+t Standard Emacs beep
+file name Play this sound file, fall back to beep"
+ :group 'org-time
+ ;; type is equivalent to `org-clock-sound'
+ :type '(choice
+ (const :tag "No sound" nil)
+ (const :tag "Standard beep" t)
+ (file :tag "Play sound file")))
+
;;;###autoload
(defun org-timer-start (&optional offset)
"Set the starting time for the relative timer to now.
@@ -400,6 +419,7 @@ replace any running timer."
(let* ((mins (string-to-number (match-string 0 minutes)))
(secs (* mins 60))
(hl (cond
+ ((stringp org-timer-message) org-timer-message)
((string-match "Org Agenda" (buffer-name))
(let* ((marker (or (get-text-property (point) 'org-marker)
(org-agenda-error)))
@@ -429,7 +449,7 @@ replace any running timer."
(run-with-timer
secs nil `(lambda ()
(setq org-timer-current-timer nil)
- (org-notify ,(format "%s: time out" hl) t)
+ (org-notify ,(format "%s: time out" hl)
,org-timer-clock-sound)
(setq org-timer-timer-is-countdown nil)
(org-timer-set-mode-line 'off)
(run-hooks 'org-timer-done-hook))))
