A watch (100) for use in a time-dependent authentication system, said watch (100) comprising: a mechanism having one or more moving components to measure and/or indicate passage of time, such as hands; a sensor subsystem (101, 102) configured to sense a mechanical configuration of said one or more moving components with respect to the fixed watch dial and to generate an output signal indicative of said sensed mechanical configuration; and a transmitter (107) configured to transmit said signal for use as a predictable, time-variant authentication token dependent on the mechanical configuration of the watch (100). In other words, the time-varying authentication token is related to the time-varying pattern formed by the positions of the hands onto the watch dial. The output signal is measured using a capacitive, an ultrasonic or an optical probe.
