A telecoil is a small coil of wire inside some hearing aids that allows the hearing aid to detect magnetism and transmit sounds generated by assistive listening systems, like those found in theaters, auditoriums, and stadiums. Telecoils were originally used to improve phone calls for hearing aid users but now provide clearer sound from assistive listening systems. Larger hearing aids are more likely to have telecoils, which provide superior sound quality over acoustic transmission and allow users to access assistive listening systems.