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;