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 procedure Hotkey(var Message: TMessage); message WM_HOTKEY;

implementation

const HK_CTRL_A: Cardinal = $ff + Ord('A');

procedure TForm1.FormActivate(Sender: TObject);
begin
 RegisterHotkey(Handle, HK_CTRL_A, MOD_CONTROL, HK_CTRL_A - $ff);
end;

procedure TForm1.Hotkey(var Message: TMessage);
begin
 if (Message.LParamLo = MOD_CONTROL) and (Message.LParamHi = HK_CTRL_A - $ff) then begin
  // do what you want
  end;
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
 UnregisterHotkey(Handle, HK_CTRL_A);
end;