Electret Condenser Mic

I'm trying to figure out how to wire up a basic electret microphone element from Radioshack:

http://comingsoon.radioshack.com/electre­t-microphone-element-with-leads/2700092.­html

I'm not sure how to wire it up to A5 on my Espruino Pico to monitor audio. I'm using a 9V battery as a power source on a breadboard and placing the output on the A5, and then also supplying BAT_IN with the same power source and GND to the negative terminal on the battery. When wired up, I get constant values so I must be doing something wrong.

Here's the code I'm using:

console.log("BEGIN");

var on = false;

setInterval(function(){
  var a = analogRead(A5);
  console.log(a.toFixed(2));
  if(a > 0.5){
    on = !on;
    LED1.write(on);
  }
}, 100);