To specify the second (more simple) solution phjr proposed:
Have a file version.txt
on your own public server and include the following function into your deployed project/script:
define('REMOTE_VERSION', 'http://your.public.server/version.txt');
// this is the version of the deployed script
define('VERSION', '1.0.1');
function isUpToDate()
{
$remoteVersion=trim(file_get_contents(REMOTE_VERSION));
return version_compare(VERSION, $remoteVersion, 'ge');
}
version.txt
should just contain the most recent version number, e.g.:
1.0.2