This circuit generates a siren sound. It was found in the April 1969 Radio Electronics magazine. The output signal is to be applied to an external amplifier.
This simple 555 biofeedback circuit was found in the December 1983 issue of Radio Electronics...
This circuit has a programmable alarm that can be triggered with different water levels. The...
Found in a 1991 Hobbyst Handbook, this circuit monitors both battery and alternator voltage. The set...