The Single T-Coil Headset with Mic for Cordless phone
T-coil works with the telecoil circuit, 95% of western hearing aids have a telecoil circuit.. Telecoil circuits receive magnetic sound. The telecoil circuit allows the hearing aid wearer to hear extremely clearly even with loud background noise.

First the T-Coil receives sound from a mobile cell phone. This sound is then transmitted magnetically by the T-Coil to the hearing aids telecoil circuit. And talking to the mic on t-coil to make conversation