jQuery – Detect value change on hidden input field

I have a hidden text field whose value gets updated via an AJAX response.

<input type="hidden" value="" name="userid" id="useid" />

When this value changes, I would like to fire an AJAX request. Can anyone advise on how to detect the change?

I have the following code, but do not know how to look for the value:

$('#userid').change( function() {  
    alert('Change!'); 
})