From 2007.igem.org

The logic principle of our design is shown above. Unless the input signal transfer from one stable condition to another ( such as 0 to 1 or 1 to 0), the output signal would change into 1, otherwise it would maintain 0. Thus, the immediate response to emergency (input change) enables our design to detect signal variation in a short time, which is beneficial for process control because of its time-saving character.