You want .change instead of .click. Assuming the select has the id: 'demo2':
$(document).ready(function () {
$('#demo2').change(function () {
$.blockUI({
css: {
border: 'none',
padding: '15px',
backgroundColor: '#000',
'-webkit-border-radius': '10px',
'-moz-border-radius': '10px',
opacity: .5,
color: '#fff'
}
});
setTimeout($.unblockUI, 2000);
});
});