This is a transistor flip-flop suggested by General Electric in a 1966 paper. The transistors are of the time and can be used equivalents.
This circuit makes use of a low impedance microphone. The relay is according to the supply voltage...
This circuit was found in an old Radio Electronics, but can still be assembled as the components are...
Any small sound amplifier from 200mW to 1W can be used in this simple circuit. Or circuit of two...