[Alegun]

Попробуйте вот это

Код:

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 

            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;

(Drkb 01334) возможно, отобразит

Добавлено немного позже

Можно ещё в принципе таймером следить за Screen.MonitorCount, если оно > 1, то значит сейчас в системе два экрана, но это правда как-то не совсем по-прогерски