Found on 90's Popular Electronics, this circuit triggers when the microphone picks up a sound. The circuit is powered by 9 V but will also work at 12 V by triggering a relay instead of the buzzer.
This squelch is activated by its own noise, acting automatically. It is used in communications...
This circuit for a simple alarm system was suggested in an article in Electronics Now magazine. The...
Found in American documentation from the 70s, this circuit uses components of the time, uncommon...