The following circuit is the simplest spybug circuit you can get. You can receive the audio through a radio or a FM receiver. The circuit transmits at 90MHz.
Step 1: Making of Spybug
Connect the emitter of transistor in between the 6 turns of the coil and 15 turns of the coil. The coil is wound on a 3mm drill and uses 0.5mm wire. The transistor turns on via the 47k and this puts a pulse through the 15 turn winding. The magnetic flux from this winding passes through the 6 turn winding and into the base of the transistor via the 22n capacitor. This pulse is amplified by the BC547 transistor and the circuit is kept active. The frequency is determined by the 6 turn coil. By moving the turns together, the frequency will decrease. The circuit transmits at 90MHz. However its range is less and consumes 16mA. Try not to touch the apparatus as it will affect the frequency. Follow the instructions as given in the image.