Techniques for facilitating a similarity search of digital assets are described. The organic light emitting device of the present invention has a lower electrode, an organic thin film layer and an upper electrode successively formed on the substrate. The security tag also includes a transmitter designed to covertly transmit security tag data to a receiver. The first condition is that a number of cell reselections being performed within a predefined first period is greater than or equal to a predefined first threshold.