Cool! DD has just R1 (or maybe R2; it's one of the traces between BS and beta) connected to the base of a transistor via a 100K resistor. The collector goes to battery -, and the emitter goes to one lead of the piezo. The other lead is connected to battery +. There is also a coil across the piezo. I guess that was louder than using R1 and R2, and justified the cost of the resistor and transistor.
