If your website is under construction, you can simply edit .htaccess file to disallow visits to your website.
Here is the code :
<Limit GET POST PUT>
order deny,allow
deny from all
allow from 12.345.67.890
</Limit>
allow from 12.345.67.890 command allows access to your server only from 12.345.67.890 IP address.
You can allow more IP’s to access your website :
<Limit GET POST PUT>
order deny,allow
deny from all
allow from 12.345.67.890
allow from 890.67.345.12
</Limit>
This practice is good in case you are modifying your website (performing a new joomla installation) and don’t want others to see the process.
Original source: http://htaccessfile.com/htaccess-allow-ip-addresses