Angler's bait indicator

The indicator shows when a fish has taken the bait. Until that happy moment (at least for the angler), the bite sensor is open, so that both LEDs are out. When a fish has been hooked, the sensor closes the current loop, where upon both LEDs light. In addition to these diodes, a buzzer may be used to give an audible signal. D2 continues to light, even when the sensor has been reopened, for as long as the thyristor has no hold current. In this way, each tug on the hook line is Indicated by D1.