Basically I'm about to start work on a site and I'd like something that I can add into my .htaccess file (or elsewhere) that'll work like this pseudo code: (my ip will be in place of 127.0.0.1)
if (visitors_ip <> 127.0.0.1)
redirectmatch ^(.*)$ http://www.example.com/under-construction.html
Hopefully that makes sense...