RewriteEngine On RewriteRule !^maintenance.php$ /maintenance.php [R=302,L]Doing so, any access to the site would be redirected to maintenance.php (which you can set up as needed with a courtesy message to the user)
If you want put a site in maintenance mode but leave it active for you only, restricting the access to your own IP, you can edit the .htaccess so (substituing 123.123.123.123 with your own IP):
RewriteEngine On
RewriteCond %{REMOTE_ADDR} !^123\.123\.123\.123$
RewriteRule !^maintenance.php$ /maintenance.php [R=302,L]