It is a remote light sensor.
It consists of a transmitter and a receiver.
The receiver is light a normal radio except that the output is shown in an LED instead of a speaker.
The transmitter transmits a tone. The frequency of that tone is based on the amount of light fallong on the CDS cell.
It seems that most oscillators carry a high pitch with lower resistance values. I want the exact opposite of this.
If you still don't understand, please tell me how I can make a long range transmitter using only BJT transistors, resistors, capacitors, and inductors, and an antenna. The transmitter must be able to produce an extremely high pitched sound in darkness (when the resistance of the cell is high) and a low pitched sound in bright light (when the resistance of the cell is low).