How to make a page unsearchable in blog search?

function hide_from_search($qry) {
  if (is_search()) $qry->query_vars['post__not_in'][] = xXx;
  return $qry;
}
add_filter('pre_get_posts','hide_from_search');

The xXx is the ID number of the page to exclude. Just read it out of the URL on the backend. When you are editing the page you want to exclude look at the URL bar. You should see “post=xXx” in there.