This project can be used as a PA amplifier, auxiliary amp, bug, intercom, etc.  The instructions show various ways to connect this kit to fit your application.  You can connect a second speaker (not included) and use it as a two-way intercom.

Components:  resistor, potentiometer, 4 capacitors, IC, microphone, speaker, transformer, 3 slide switches, battery snap

Principles taught:  operational amplifiers, security, audio