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function IsHandleActive(Handle: HWND): boolean;
var
  buf: Array[0..1024] of char;
  str: string;
begin
  result := false;
  windows.GetWindowText(handle, @buf, sizeof(buf));
  str := buf;
  if findwindow(nil, pchar(str)) <> 0 then
    result := true;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  if IsHandleActive(Form1.Handle) then
    showmessage('Is Active!');
end;