The EKI 2018 Fish Caller Kit produces a clicking sound similar to that made by a dying fish.
Put the completed kit in a watertight container and suspend from the boat or dock into the water. Hungry fish come to investigate. 1.5V battery and connector not included. Principles taught: transistor oscillator. Components: resistor, capacitor, slide switch, transistor, audio transformer, potentiometer, crystal microphone (used as speaker).