Improve code for detecting USB drive insertion & removal

Dear Experts,
Please refer to the included code which detects when a USB device is connected or disconnected.
It worked perfectly for me. As you can see it handles the Windows message WM_DEVICECHANGE.
However as it stands its not that flexible for easily adding to a project..

It would be nice to have this in a self-contained unit that generates suitable events when a USB device is attached or removed. I would prefer that it not be made into a component that I have to install, in order  to produce more portable code.

I don't know if its possible to handle a message without a form, but maybe it could be a small non-visible dummy form.

If it seems possible I would appreciate a working Delphi 5 compatible version.
Many thanks!

unit USBDetectF;
{taken from an Experts Exchange solution:
 http://www.experts-exchange.com/Programming/Languages/Pascal/Delphi/
                             Q_21552015.html?sfQueryTermInfo=1+drive+letter+usb
 ginsonic:
 Here is a complete sample project. Use a form and a label.
}
 
interface
 
uses
  Windows, Messages, Classes, Forms, Controls, StdCtrls, Buttons;
 
type
  TUSBDetectForm = class(TForm)
    Label1: TLabel;
    BitBtn1: TBitBtn;
    Label2: TLabel;
    Label3: TLabel;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  protected
    procedure   WMDEVICECHANGE(var Msg: TMessage); message WM_DEVICECHANGE;
  public
    { Public declarations }
  end;
 
var
  USBDetectForm: TUSBDetectForm;
 
{----------------------------------------------------------------------------}
// Device constants
const
  DBT_DEVICEARRIVAL          =  $00008000;
  DBT_DEVICEREMOVECOMPLETE   =  $00008004;
  DBT_DEVTYP_VOLUME          =  $00000002;
 
// Device structs
type
  _DEV_BROADCAST_HDR         =  packed record
     dbch_size:              DWORD;
     dbch_devicetype:        DWORD;
     dbch_reserved:          DWORD;
  end;
  DEV_BROADCAST_HDR          =  _DEV_BROADCAST_HDR;
  TDevBroadcastHeader        =  DEV_BROADCAST_HDR;
  PDevBroadcastHeader        =  ^TDevBroadcastHeader;
 
type
  _DEV_BROADCAST_VOLUME      =  packed record
     dbch_size:              DWORD;
     dbch_devicetype:        DWORD;
     dbch_reserved:          DWORD;
     dbcv_unitmask:          DWORD;
     dbcv_flags:             WORD;
  end;
  DEV_BROADCAST_VOLUME       =  _DEV_BROADCAST_VOLUME;
  TDevBroadcastVolume        =  DEV_BROADCAST_VOLUME;
  PDevBroadcastVolume        =  ^TDevBroadcastVolume;
 
implementation
{$R *.dfm}
 
procedure TUSBDetectForm.WMDEVICECHANGE(var Msg: TMessage);
var  lpdbhHeader:   PDevBroadcastHeader;
     lpdbvData:     PDevBroadcastVolume;
     dwIndex:       Integer;
     lpszDrive:      String;
begin
 
  // Perform inherited
  inherited;
 
  // Get the device notification header
  lpdbhHeader:=PDevBroadcastHeader(Msg.lParam);
 
  // Handle the message
  lpszDrive:='Drive ';
  case Msg.WParam of
     DBT_DEVICEARRIVAL       :    {a USB drive was connected}
     begin
        if (lpdbhHeader^.dbch_devicetype = DBT_DEVTYP_VOLUME) then
        begin
           lpdbvData:=PDevBroadcastVolume(Msg.lParam);
           for dwIndex :=0 to 25 do
           begin
              if ((lpdbvData^.dbcv_unitmask shr dwIndex) = 1) then
              begin
                 lpszDrive:=lpszDrive+Chr(65+dwIndex)+':';
                 break;
              end;
           end;
           Label1.Caption:=lpszDrive + ' connected';
        end;
     end;
     DBT_DEVICEREMOVECOMPLETE:    {a USB drive was removed}
     begin
        if (lpdbhHeader^.dbch_devicetype = DBT_DEVTYP_VOLUME) then
        begin
           lpdbvData:=PDevBroadcastVolume(Msg.lParam);
           for dwIndex:=0 to 25 do
           begin
              if ((lpdbvData^.dbcv_unitmask shr dwIndex) = 1) then
              begin
                 lpszDrive:=lpszDrive+Chr(65+dwIndex)+':';
                 break;
              end;
           end;
           Label1.Caption:=lpszDrive + ' removed';
        end;
     end;
  end;
end;
 
procedure TUSBDetectForm.FormCreate(Sender: TObject);
begin
  Label1.Caption := '';
end;
 
end.

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