var audio = new Audio("alarm.wav");
audio.play();

document.write('<audio id="player" src="alarm.wav" >');
document.getElementById('player').play();

{
  "name": "Alarm",
  "version": "1.0.0",
  "icons": {"64": "icon64.png"},
  "permissions": [
    "http://site1/",
    "http://site2/"
  ],
  "content_scripts": [
    {
      "matches": ["http://site1/", "http://site2/"],
      "js": ["myscript.js"],
      "run_at": "document_end"
    }
  ],
  "manifest_version": 2
}

var myAudio = new Audio();
myAudio.src = "alarm.mp3";
myAudio.play();

var myAudio = new Audio();        // create the audio object
myAudio.src = "path/to/file.mp3"; // assign the audio file to its src
myAudio.play();                   // play the music