This circuit was published in the July 1993 issue of Electronics Now magazine. It uses a sensor from the time and triggers a buzzer with a Sonalert-type oscillator.
The critical component of this circuit is the transformer. T1 and T2 can be BD135 and T3 / T4 can...
The figure shows how to implement an R-S flip-flop or bistable reset-Set with an LM3900...
This circuit was found in a 1987 documentation but uses components quite common in the current...