buzzer bz used as an electronic chime is connected between the output terminal out and the ground an alarm pulse a indicative of an alarm as shown by a in fig2 b is applied to the first input terminal in 1 and a reference clock signal b as shown by b in fig2 b is applied to the second input terminal in 2 in operation the alarm pulse signal a and the reference clock signal b are both applied to the first and second input terminals in 1 and in 2 respectively when the alarm pulse signal a rises to a high voltage level since the transistor 1 is turned on the positive terminal of the capacitor 3 drops down to the ground level because an electric charge stored in the capacitor 3 is discharged via the diode 4 on the other hand when the alarm pulse a falls since the transistor 1 is turned off a supply voltage vcc is supplied to the positive terminal of the capacitor 3 via a resister r 2 to start charging up the capacitor 3 under these conditions while the second transistor 2 is turned off no current flows through the capacitor 3 so that a supply voltage difference vcc develops across the capacitor.