The most obvious alarm indication is a flashing light.This requires relatively complex electronics. however, to achieve correct flash-ing. Moreover, in certain circumstances, such as when the lamp is in bright light. -Lie indicator cannot be seen properly.
The present circuit is simplicity itself: it consists of only three components and provides not only a visual but also an audible indication. It is based on a special LED that contains the electronics to ensure that it lights periodically. When the LED is on, it draws a much larger current than in its quiescent state. This property is used to good effect. When the LED is out, hardly any current flow so that there is no voltage across the buzzer. When the LED is on, the relatively large current causes a drop across the buzzer, so that this sounds. The capacitor across the LED ensures sufficient butTering (decoupling) of the voltage across the diode. The circuit is actuated when a direct voltage of 7-9 V is applied to it.
The circuit draws a current of about 10 mA.