That be On After Delay Circuit. I uses mosfet in the circuit for delay easy more than the transistor. By have the work of the circuit be when press , S1 , an electric bell will not loud suddenly , must wait for follow the period of time that note. The Q2 will get back to the position or Status of Q1. Thus electronics bell will loud immediately after. The time haded delaied until finish already. If enhance the value C1 while delaied long go up. Note: Rs add keep for decrease the popularity of an electric bell , R1 add keep for decrease the time down and decrease the noise give Mosfet. The Q2 use 2N2222 or BC549 or C1815. The circuit is simple this , friends may like , request enjoy please sir.