[DllImport("WinScard.dll", EntryPoint = "SCardListReadersA", CharSet = CharSet.Ansi)]

    static extern int SCardListReaders(

        ret = SCardListReaders(hContext, null, null, ref pcchReaders);

        ret = SCardListReaders(hContext, null, mszReaders, ref pcchReaders);

  [DllImport("winscard.dll", EntryPoint="SCardListReadersA", CharSet=CharSet.Ansi)]

    public static extern int SCardListReaders(

if you invoke SCardListReaders with the hContext parameter set to null, you'll get the list of the installed readers (not the plugged ones !)

ret = SCardListReaders(hContext,IntPtr.Zero,null,ref pcchReaders);

ret = SCardListReaders(hContext,IntPtr.Zero ,mszReaders, ref pcchReaders);