How do I detect when a button is clicked?

How do I detect when a button is clicked?

<script src="jquery.js"></script>
<script>
$(document).ready(function(){
        $("#Alert").click(function(){
            alert("Message");
        });
    });
</script>
<button id="Alert" class="<?php echo $variable; ?>">Click button</button>

This didn't work... Did I do anything wrong?