PURPOSE: To sense a light shock applied to a door to chime a doorbell by attaching a piezoelectric element, which detects the shock from the external, to a door itself and electrically using the piezoelectric voltage generated by the piezoelectric element as the trigger signal of doorbell chiming.

CONSTITUTION: The light shock like a knock applied to the door is sensitively detected by a piezoelectric element 10, and an output transistor TR 38 is operated by the piezoelectric voltage generated at this time, and this output is amplified by an amplifier 26 and charges a capacitor 36. Consequently, the output TR 38 is turned on by the sufficiently high charging voltage of the capacitor 36, and a chime circuit 120 fulfills the sure chiming function at the time of detection. The charged electric charge of the capacitor 36 is discharged by the discharge path formed at the time of turning-on of the output TR 38. Thus, the doorbell is chimed for a preliminarily determined certain time.