[NumLock]

Код:

type
  TButton = class(StdCtrls.TButton)
  public
    property OnMouseWheel;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure MouseWheelEventHandler(Sender: TObject; Shift: TShiftState;
      WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
  end;
...
procedure TForm1.FormCreate(Sender: TObject);
begin
  Button1.OnMouseWheel:=MouseWheelEventHandler;
end;

procedure TForm1.MouseWheelEventHandler(Sender: TObject; Shift: TShiftState;
  WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
begin
  Windows.Beep(1000, 250);
end;