If you are looking to get into the spy game have a look at your first gadget you need here, it is a Mini FM Transmitter.
“It transmits FM waves so you could easily receive the signals on your mobile phone, radios, etc. As the name and the picture indicates it is very small and is approximately the size of a 9v battery clip. With this FM transmitter you could start your own mini FM station. The circuit uses BC547 transistor to amplify the signal and then frequency modulate it. It uses “frequency modulation” most commonly known as FM, the same principal to transmit audio signals captured by the microphone.
Components
BC547 Transistor
An microphone
A variable capacitor 47pf
An Inductor (see steps for description)
4.7k Resistor
330ohm resistor
1n capacitor (102)
10p capacitor
9V battery
LED(optional) “