FM systems consists of a transmitter and a receiver.

The receiver is connected to the CI-processor. The same receiver can also be connected with most conventional hearing aids.

The transmitter picks up the sound (e.g. from the teacher's voice, from the television or the cell-phone) and sends it via radio waves, wirelessly, directly to the tiny receiver.  This enhances the sound quality in difficult listening situations (like in noise or at a distance)