A radio earpiece generally has three functions:
(Transducer) which lets you hear incoming radio traffic. These can be in many styles; sitting outside the ear, inside the ear or inside and ear-defender for instance. It may even be a covert Inductive loop type.
Acoustic Tube Earpieces
Acoustic Tube earpieces are the most popular covert type of earpiece. A clear tube transfers sound generated in the transducer clipped to the users collar via the tube into the users ear.