Check if Wordpress sidebar widget area is empty or not

count_widgets_in_sidebar.php

function count_widgets_in_area($area) {
    $widgets = get_option('sidebars_widgets');
    if(isset($widgets[$area])) {
        return count($widgets[$area]);
    }
    return null;
}

if(!is_null(count_widgets_in_area("area_id"))) {
  // there are some widgets 
} else {
  // widget area is empty
}