How to detect if any key is pressed

public static IEnumerable<Key> KeysDown()
{
    foreach (Key key in Enum.GetValues(typeof(Key)))
    {
        if (Keyboard.IsKeyDown(key))
            yield return key;
    }
}

you could then do:

if(KeysDown().Any()) //...

If you want to detect key pressed only in our application (when your WPF window is activated) add KeyDown like below:

public MainWindow()
{
    InitializeComponent();
    this.KeyDown += new KeyEventHandler(MainWindow_KeyDown);
}

void MainWindow_KeyDown(object sender, KeyEventArgs e)
{
    MessageBox.Show("You pressed a keyboard key.");
}

If you want to detect when a key is pressed even your WPF window is not active is a little harder but posibile. I recomend RegisterHotKey (Defines a system-wide hot key) and UnregisterHotKey from Windows API. Try using these in C# from pinvoke.net or these tutorials:

• Global Hotkeys: Register a hotkey that is triggered even when form isn't focused.
• Simple steps to enable Hotkey and ShortcutInput user control

Thse is a sample in Microsoft Forums.

You will use Virtual-Key Codes. I Hope that I was clear and you will understand my answer.