Как корректно определить изменения в оборудовании Plug & Play?

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 

{$R *.DFM} 

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;