{
 Some applications need to know when the user inserts or
 removes a compact disc or DVD from a CD-ROM drive without
 polling for media changes. Windows provide a way to notify these
 applications through the WM_DEVICECHANGE message.
}
 type
  TForm1 = class(TForm)
  private
  procedure WMDeviceChange(var Msg: TMessage); message WM_DEVICECHANGE;
  public
  end;
 {...}
 implementation
 {$R *.DFM}
 procedure TForm1.WMDeviceChange(var Msg: TMessage);
 const
  DBT_DEVICEARRIVAL = $8000; // system detected a new device
 DBT_DEVICEREMOVECOMPLETE = $8004; // device is gone
var
  myMsg: string;
 begin
  inherited;
  case Msg.wParam of
  DBT_DEVICEARRIVAL: myMsg := 'CD inserted!';
  DBT_DEVICEREMOVECOMPLETE: myMsg := 'CD removed!';
  end;
  ShowMessage(myMsg);
 end;

 {*********************************************}
 // Advanced Code:
// When the device is of type volume, then we can get some device specific
// information, namely specific information about a logical volume.
// by Juergen Kantz
unit Unit1;
 interface
 uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 type
  TForm1 = class(TForm)
  Button1: TButton;
  label1: TLabel;
  private
  procedure WMDeviceChange(var Msg: TMessage); message WM_DeviceChange;
  { Private declarations }
  public
  { Public declarations }
  end;
 const
  DBT_DeviceArrival = $8000;
  DBT_DeviceRemoveComplete = $8004;
  DBTF_Media = $0001;
  DBT_DevTyp_Volume = $0002;
 type
  PDevBroadcastHdr = ^TDevBroadcastHdr;
  TDevBroadcastHdr = packed record
  dbcd_size: DWORD;
  dbcd_devicetype: DWORD;
  dbcd_reserved: DWORD;
  end;
 type
  PDevBroadcastVolume = ^TDevBroadcastVolume;
  TDevBroadcastVolume = packed record
  dbcv_size: DWORD;
  dbcv_devicetype: DWORD;
  dbcv_reserved: DWORD;
  dbcv_unitmask: DWORD;
  dbcv_flags: Word;
  end;
 var
  Form1: TForm1;

 implementation
 {$R *.dfm}

 function GetDrive(pDBVol: PDevBroadcastVolume): string;
 var
  i: Byte;
  Maske: DWORD;
 begin
  if (pDBVol^.dbcv_flags and DBTF_Media) = DBTF_Media then
  begin
  Maske := pDBVol^.dbcv_unitmask;
  for i := 0 to 25 do
  begin
  if (Maske and 1) = 1 then
  Result := Char(i + Ord('A')) + ':';
  Maske := Maske shr 1;
  end;
  end;
 end;
 procedure TForm1.WMDeviceChange(var Msg: TMessage);
 var
  Drive: string;
 begin
  case Msg.wParam of
  DBT_DeviceArrival:
  if PDevBroadcastHdr(Msg.lParam)^.dbcd_devicetype = DBT_DevTyp_Volume then
  begin
  Drive := GetDrive(PDevBroadcastVolume(Msg.lParam));
  label1.Caption := 'CD inserted in Drive ' + Drive;
  end;
  DBT_DeviceRemoveComplete:
  if PDevBroadcastHdr(Msg.lParam)^.dbcd_devicetype = DBT_DevTyp_Volume then
  begin
  Drive := GetDrive(PDevBroadcastVolume(Msg.lParam));
  label1.Caption := 'CD removed from Drive ' + Drive;
  end;
  end;
 end;

 end.