<select id="Select1" name="Select1">
<option>---</option>
<option value="1">1</option>
<option value="2">2</option>
</select>


    <script type='text/javascript'>
        $(function () {
            $('select').change(function () {
                if ($('select').length == $('select option:selected').length)
                    alert('x');
            }
            );
        });
    </script>