Spy Bug FM Transmitter
It is a two transistor Spy
Transmitter that will send the sounds picked up in a room to any FM radio tuned to the same frequency as the transmitter. Resistors, capacitors, and even the wire needed to wind the small coil can also be salvaged from an old circuit board.
This tutorial shows on how you can make your own spy bug that will transmit audio through a FM transmitter that will require a few parts from an electronic supply store and a fair amount of experience in using a soldering iron on small electronic parts.
The spy phone
transmitter consists of two sections, namely, automatic switching section and FM transmitter section.