nagios-apt-watch is a plugin for the popular
Nagios monitoring program.
It can monitor the status of all packages installed on a system via APT. The plugin triggers a warning, when one ore more packages are needed to be upgraded.
You can download the current version of the plugin from the Files Secion: http://alioth.debian.org/project/showfiles.php?group_id=31002
Please be aware that this is an early version, which isn't guaranted to work on every system nor is bug-free or feature complete.
Please consider reading the Installation Manual before starting to use this software. For remote invocation via NRPE, there's an additional guide: README_NRPE.txt. For questions about the plugin, I recommend using the Forums.
The project's primary source code management system is Alioth's SVN repository. You can access the repository via web at http://svn.debian.org/wsvn/nagios-aptwatch/
The plugin is hosted by Debian's Alioth service. Further information can be found on the project's Gforge pages.