Talk Through Your Ears earpieces may function in a listen-only format when plugged into a lapel speaker mic; however, volume limitation is not available in this scenario and audio performance may be unsatisfactory.  Talk Through Your Ears earpieces are volume-limited only when interfaced with the Talk Through Your Ears control unit. CavCom's RadioGear earsets are also volume-limited and are designed specifically for use with lapel speaker microphones.