offline mode

Hi,

i´m looking for the offline modus. I uploaded two plug ins without working. Now I triad to put in this sequence:
function wp_website_wartungsmodus() {

if (!current_user_can(“edit_themes”) or !is_user_logged_in()) {
wp_die(“Wartungsmodus!
\n”.
“Der Blog ist in Kürze wieder erreichbar.\n”);
}
}
add_action(‘get_header’, ‘wp_website_wartungsmodus’);

But too without working.
I triad to brin it in the “function php” but where du I have to put it in?

Please someone can show me the sentence bevore or after?

Many thanks and looking forward
hunter2