Как корректно определить изменения в оборудовании PlugNPlay?

Code:

type

              TForm1 = class(TForm)

                Button1: TButton;

              private

                { Private declarations }

                procedure WMDeviceChange(var Message: TMessage);

                  message WM_DEVICECHANGE;

              public

                { Public declarations }

              end;

            var

              Form1: TForm1;

            implementation

            {$R *.DFM}

            const DBT_DEVICEARRIVAL = $8000;

            const DBT_DEVICEQUERYREMOVE = $8001;

            const DBT_DEVICEQUERYREMOVEFAILED = $8002;

            const DBT_DEVICEREMOVEPENDING = $8003;

            const DBT_DEVICEREMOVECOMPLETE = $8004;

            const DBT_DEVICETYPESPECIFIC = $8005;

            const DBT_CONFIGCHANGED = $0018;

            procedure TForm1.WMDeviceChange(var Message: TMessage);

            var

              s : string;

            begin

            {Do Something here}

              case Message.wParam of

                DBT_DEVICEARRIVAL :

                  s := 'A device has been inserted and is now available';

                DBT_DEVICEQUERYREMOVE: begin

                  s := 'Permission to remove a device is requested';

                  ShowMessage(s);

                 {True grants premission}

                  Message.Result := integer(true);

                  exit;

                end;

                DBT_DEVICEQUERYREMOVEFAILED :

                  s := 'Request to remove a device has been canceled';

                DBT_DEVICEREMOVEPENDING :

                  s := 'Device is about to be removed';

                DBT_DEVICEREMOVECOMPLETE :

                  s := 'Device has been removed';

                DBT_DEVICETYPESPECIFIC :

                  s := 'Device-specific event';

                DBT_CONFIGCHANGED :

                  s:= 'Current configuration has changed'

                else s := 'Unknown Device Message';

              end;

              ShowMessage(s);

              inherited;

            end;