private
    { Private declarations }
    Aatom: ATOM;
    procedure hotkey(var msg: TMessage); message WM_HOTKEY;

procedure TForm1.FormCreate(Sender: TObject);
begin
  if FindAtom('ZWXhotKey') = 0 then
  begin
    Aatom := GlobalAddAtom('ZWXhotKey');
  end;
  if RegisterHotKey(Handle, Aatom, MOD_ALT, $41) then
  begin
    MessageBox(Handle, '按alt+a', '提示', MB_OK);
  end;
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  UnregisterHotKey(Handle, Aatom);
  GlobalDeleteAtom(Aatom);
end;

procedure TForm1.hotkey(var msg: TMessage);
begin
  if (msg.LParamHi = $41) and (msg.LParamLo = MOD_ALT) then
  begin
    showmessage('Ctrl+A');
  end;
end;