This circuit was suggested by Motorola in a 1969 publication. It makes use of components of the time, but both the FET and the bipolar may be general purpose current types.
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...