The capabilities detection tool will analyse your assemblies and give you each of the capabilities that your app has. It's a good idea to do this when changing, adding or removing major functionality to your app just so you know what is going to be displayed as requirements for your application in zune.
Every time i use this function i have to hunt for how to do it, so i thought I'd make a little guide.
I've created a little script that will run the cap detect tool. Double check the paths to the Cap Detect files and you'll need to change the path highlighted in red to your applications Bin\Debug directory. Save this with a .bat extension.
set PATH="C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.0\Tools\CapDetect\"
CapabilityDetection.exe "C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.0\Tools\CapDetect\Rules.xml" "E:\Metro Match\Bin\Debug"
Run this file and you should get something like this:
Then find your WMAppManifest.xml file in the properties folder of you main startup project.
Now make sure the capabilities match those in the capabilities detection tool.