addEventListener using a button doesn't do anything

Playing around with some Javascript and I'm trying to display the clock when a button is clicked. Using just the js without addEventListener works, it displays the clock in the target div. When I add addEventListener though, nothing happens. I'm quite new to programming and often overlook some typos and syntax errors but I've been through this many times and didn't find anything.

This is the js code:

   document.addEventListener('DOMContentReady', function () {
    document.getElementById('clock-button').addEventListener('click', startClock, false);
});

function startClock() {
    var today = new Date();
    var h = today.getHours();
    var m = today.getMinutes();
    var s = today.getSeconds();

    m = checkTime(m);
    s = checkTime(s);

    document.getElementById('clock').innerHTML = h + ":" + m + ":" + s;
    t = setTimeout(function () {
        startClock();
    }, 500);

    console.log("works");
}

function checkTime(i) {
    if (i < 10) {
        i = "0" + i;
    }

    return i;
}

And the jsfiddle here: http://jsfiddle.net/Em46R/1/

Replace DOMContentReady with DOMContentLoaded