Secunia PSI 2 is a powerful tool that not only detects missing security patches on your PC, but in some cases can download and install them for you, entirely automatically.
The process starts when you launch the program and initiate a scan. PSI 2 will immediately build a list of your installed applications and their versions, compare these with an online database, and let you know about any updates that might be available.
There are other apps that do something similar, of course, but here's where PSI 2 takes a lead. Not only does will the program tell you that, say, your copy of Firefox is out-of-date: it's also able to download and install the new version all on its own, while you get on with more important things.
The program will only automatically update a few applications at the moment: the Flash player, Adobe Reader, Firefox, Foxit Reader, Skype, Java and so on. Still, it's only a beta, so that's no surprise. But even now there's enough coverage to be useful, especially as PSI 2 can also help you out with many other updates.
It wasn't able to automatically patch our outdated version of VLC Media Player, for instance, but did provide an Install Solution button instead. Clicking this downloaded the new version, without us having to manually open a browser window and locate it manually, saving a little time and hassle.
And if you leave Secunia PSI 2 running in the background, then it will periodically check for application updates, and let you know when your system requires an update. We're not so sure about this part of the program, though, as its RAM use is a little high (over 80MB on our system). That may be beta-related, too, but for now you're probably better off running manual scans, maybe once a day.