On Windows, PlayerPrefs are stored in the registry under HKCU\Software\[company name]\[product name] key, where company and product names are the names set up in Project Settings.
On Linux, PlayerPrefs can be found in ~/.config/unity3d/[CompanyName]/[ProductName] again using the company and product names specified in the Project Settings.
On Windows Store Apps, Player Prefs can be found in %userprofile%\AppData\Local\Packages\[ProductPackageId]>\LocalState\playerprefs.dat
On Windows Phone 8, Player Prefs can be found in application's local folder, See Also: Windows.Directory.localFolder
On Android, you'll have to have your device rooted. Rooting is necessary to be able to access the data - Partition.You can find the PlayerPrefs' XML file here: /data/data/<yourpackagename>/shared_prefs/<yourpackagename>.xml"
On iOS, the PlayerPrefs can be found in your app's plist
file. It's located at:/Apps/ your app's folder /Library/Preferences/ your app's .plist