This project is also similar to the two preceding projects. However, instead of using a radiofrequency identification (RFID) tag reader or keypad, this version of the lock uses a secret knock (Figure 7-1).
FIGURE 7-1 Secret knock door lock.
The idea is that you train the lock with a certain pattern of knocks, and then, when it hears the correct knock, it releases the door. This type of lock should not be considered to be as secure as the preceding two lock projects but is a great bit of fun.
Just as with the ...