In a display device of the invention, driving of the piezoelectric element is controlled to change the light path of the propagating light inside a light guiding plate. The method includes providing a security system having at least one sensor, coupling a detected state of the at least one sensor to a web server, the web server publishing the detected state and a remotely located user subscribing to receive the detected state of the at least one sensor via the publication by the web server. By the arrangement, optically assisted magnetic recording can be performed, small size and light weight are achieved, and higher transfer rate can be implemented.