Reinstalling Windows is always a hassle, but if you've lost a few product keys then it could become a real nightmare. Are they on a CD case, a manual, in an old email somewhere? You might not be able to get your system working properly again until you can track them down.

It doesn't have to be this way, though. If you install a product key finder now, then it will scan your PC, and report on any product keys it finds (expect the list to include Windows and Microsoft Office as a minimum, and often many more). Print out the report or save it to disc and you'll always have your keys to hand, should disaster strike - much more convenient.

Which is the best product key finder, then? Good question - there's a lot of competition - but we put 10 of the best free key finders to the test in an effort to find out. Keep reading to find out what we discovered.

Belarc Advisor 8.2.7.7

Download Belarc Advisor 8.2.7.7

Total keys supported: 100+
Supported products include: Windows, Office, CyberLink apps, VMware Workstation, Nero Burning ROM

Belarc Advisor

Free for personal use only, Belarc Advisor is a powerful system information tool which builds up a very detailed picture of your PC hardware and software. This is way more than we need, but you don't have to pay attention to that information if you don't want to - just click Software Licences and you'll find keys for Windows, Office, CyberLink applications, Norton Internet Security and more.

Score: 4/5

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Free PC Audit 2.1

Download Free PC Audit 2.1

Total keys supported: 10+
Supported products include: Windows, Office

Free PC Audit

Run Free PC Audit and it'll immediately display a summary of your PC hardware, installed and running software. The program only managed to display the Windows and Office product keys on our test PC, but it could still be useful to see and save the full list of your other installed applications. The program doesn't require installation, making it convenient to use, and doesn't include annoying adware - rare amongst this type of tool.

Score: 3/5

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KeyFinder Thing 3.1.6

Download KeyFinder Thing 3.1.6

Total keys supported: 90
Supported products include: Windows 7, Office 2010, Visual Studio 2005, Adobe CS2-CS5 products

KeyFinder Thing

KeyFinder Thing is a basic key finder tool. It's a little dated now - there's coverage for Microsoft Visual Studio, for instance, but only up to 2005 - so is really only useful as a basic product checker for Windows and a few old games. Even then, the program doesn't fully work with 64-bit systems, and it comes bundled with the AVG Security toolbar for extra irritation.

Score: 1.5/5

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LicenseCrawler 1.9.255

LicenseCrawler 1.9.255

Total keys supported: 200+
Supported products include: Windows, Microsoft Office, CyberLink applications

LicenseCrawler

The free-for-personal-use LicenceCrawler takes a unusual approach to finding product keys, simply scanning the Registry and displaying likely-looking values. This can make for a complex report, sometimes including entries which aren't product keys at all, and an in-your-face nag screen is another irritation. The program can find a lot of keys, though, and these are easily saved to a text file for later reference.

Score: 3.5/5

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Magical Jelly Bean Keyfinder 2.0.8

Download Magical Jelly Bean Keyfinder 2.0.8

Total keys supported: 300
Supported products include: Windows, Office, Nero Burning Rom 5-7

Magical Jelly Bean Keyfinder

Like many of the competition, Magical Jelly Bean Keyfinder is a little out-of-date; it'll give you your Windows 7 and Office 2010 keys, but for instance couldn't display our Nero 11 key as it doesn't support anything later than Nero 7. Unusually, though, the program has an editable configuration file, so if you're willing to do some work then you may be able to add support for one or two extra keys yourself.

Score: 3/5

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MSKeyViewer Plus 2.2.0

Download MSKeyviewer Plus 2.2.0

Total keys supported: 101
Supported products include: Windows, Microsoft Office, SQL Server 7/2008, WinZip 8-14

MSKeyViewer Plus

MSKeyViewer Plus 2.2.0 is a simple tool which is mainly useful for displaying a few key Microsoft product keys: Windows, Office 97-2010, and so on. There are a few others, but these are notably getting a little dated now (there's support for WinZip 8-14, for instance, but the current version is 16.5). Still, it's portable, easy to use, and will copy your keys to the clipboard with a click for easy saving in some other document.