... 
type 
  TForm2 = class(TForm) 
    procedure FormResize(Sender: TObject); 
  private 
    { Private-Deklarationen } 
  public 
    procedure WMCAPTURECHANGED(var Msg: TMsg); message WM_CAPTURECHANGED; 
  end; 
 
var 
  Form2: TForm2; 
 
implementation 
 
{$R *.DFM} 
 
var 
  sizeflag: boolean = false; 
 
procedure TForm2.WMCAPTURECHANGED(var Msg: TMsg); 
begin 
  DefaultHandler(Msg); 
  if sizeflag then begin 
    sizeflag := false; 
    // mach was, z.B.: 
    beep; 
  end; 
end; 
 
procedure TForm2.FormResize(Sender: TObject); 
begin 
  sizeflag := true; 
end;