type 
  TForm1 = class(TForm) 
   Button1: TButton; 
  private 
   { Private declarations } 
   procedure WMDisplayChange(var Message: TMessage); 
     message WM_DISPLAYCHANGE; 
  public 
   { Public declarations } 
  end; 
 
var 
  Form1: TForm1; 
 
implementation 
 
{$R *.DFM} 
 
procedure TForm1.WMDisplayChange(var Message: TMessage); 
begin 
{Do Something here} 
  inherited; 
end;