// ==UserScript==
// @name        Clash alert
// @include     https://www.codingame.com/*
// @version     1
// @grant       none
// ==/UserScript==

var player = document.createElement('audio');
player.src = 'http://www.gravomaster.com/alarm/sounds/ding.mp3';
player.preload = 'auto';

$(document).on("DOMSubtreeModified", '.countdown', function(){
  var timer = $(this).find('.ng-binding').html();
  if (timer == "00:04")
    player.play();
});