procedure TMainForm.WMDEVICECHANGE(var Msg: TWMDeviceChange);
var
 lpdb  : PDevBroadcastHdr;
 lpdbpr: PDevBroadCastPort;
 S: string;
begin
{Заголовок сообщения}
lpdb := PDevBroadcastHdr(Msg.dwData);
case Msg.Event of
  DBT_DEVICEARRIVAL:
  begin {Добавление}
    if lpdb^.dbch_devicetype = DBT_DEVTYP_PORT then begin
      lpdbpr:= PDevBroadCastPort(Msg.dwData);
      S := StrPas(@lpdbpr.dbcp_name);

      {SetComName(S);}
    end;
  end;
  DBT_DEVICEREMOVECOMPLETE:
  begin {Удаление}
    if lpdb^.dbch_devicetype = DBT_DEVTYP_PORT then begin
      lpdbpr:= PDevBroadCastPort(Msg.dwData);
      S := StrPas(@lpdbpr.dbcp_name);

      {if S = GetComName then
      begin
        SetComName('COM1');
      end;}
    end;
  end;
end;
end;