diff --git a/.gitignore b/.gitignore
index 4d21628..81eeb92 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,4 @@ src/lib/
 .DS_Store
 src/1.js
 src/2.js
+src/audio/*.wav
diff --git a/README.md b/README.md
index d5e8b24..cad3c80 100644
--- a/README.md
+++ b/README.md
@@ -37,3 +37,7 @@ GitHub Actions are used to perform automated code quality checks upon PR creatio
 
 Spell checking via CSpell
 See `spelling.json` for custom dictionary
+
+## Credits
+
+* the notification sound `481151__matrixxx__cow-bells-01.wav` is from [freesound.org](https://freesound.org/people/MATRIXXX_/sounds/481151/)
diff --git a/scripts/sync_to_server.sh b/scripts/sync_to_server.sh
index e07a8d5..b9e2695 100755
--- a/scripts/sync_to_server.sh
+++ b/scripts/sync_to_server.sh
@@ -7,3 +7,4 @@ cd $script_dir/..
 rsync -rvhu --delete --no-perms --exclude *.test.js src/*.js entorb@entorb.net:html/eta/
 rsync -rvhu --delete --no-perms src/*.html entorb@entorb.net:html/eta/
 rsync -rvhu --delete --no-perms src/*.css entorb@entorb.net:html/eta/
+rsync -rvhu --delete --no-perms src/audio/*.mp3 entorb@entorb.net:html/eta/audio/
diff --git a/src/audio/481151__matrixxx__cow-bells-01.mp3 b/src/audio/481151__matrixxx__cow-bells-01.mp3
new file mode 100644
index 0000000..26c4986
Binary files /dev/null and b/src/audio/481151__matrixxx__cow-bells-01.mp3 differ
diff --git a/src/helper.js b/src/helper.js
index be70177..c260103 100644
--- a/src/helper.js
+++ b/src/helper.js
@@ -276,6 +276,24 @@ function read_html_input_number(html_input) {
   return Number(value_str);
 }
 
+/**
+ * play a sound of mp3 format
+ * @param {*} url of mp3 sound file
+ */
+function playSound(url) {
+  const audio = new Audio(url);
+  audio.play();
+}
+
+/**
+ * Play sound file for timer done
+ */
+function playSoundTimerDone() {
+  playSound('audio/481151__matrixxx__cow-bells-01.mp3');
+}
+
+
+
 // Export functions, needed for Jest unittests
 // Using this hack it works for both, jest and browser.
 // from https://stackoverflow.com/questions/66349868/jest-unit-testing-module-export-error-in-browser-console
@@ -295,4 +313,6 @@ module.exports = {
   calc_row_new_delta,
   sort_data,
   read_html_input_number,
+  playSound,
+  playSoundTimerDone,
 };
diff --git a/src/main.js b/src/main.js
index f7691e8..8b2ba8e 100644
--- a/src/main.js
+++ b/src/main.js
@@ -32,11 +32,14 @@ prevent entering non-numbers
 add delta1
 html placeholders
 weighted linreg instead, to put more weight on the latest items
+play notification sound when estimated time is reached
 
 TODO/IDEAS
 chart: choose to display remaining instead of items
 tabulator: use global data, and update column speed name upon switching unit
 echarts: use global data, and update speed unit
+store "hide_intro" as setting
+add simple time-only countdown+notification
 */
 
 //
@@ -178,6 +181,7 @@ function update_runtime_and_remaining() {
   let ms_remaining = total_timestamp_eta - Date.now();
   if (ms_remaining < 0) {
     ms_remaining = 0;
+    playSoundTimerDone();
     // stop timer
     clearInterval(interval_auto_refresh);
   }