T-coils have many names – T-switch, T-coil, audio coil or telephone coil. How does a T-coil work in a hearing aid/cochlear implant? It effectively turns the hearing aid or cochlear implant into your own personal sound system, allowing it to communicate directly to ALDs/PLDs, FM or infrared systems, telephones and loop systems either automatically or by the flip of a switch. Very simply, T-coils are little coils of copper wire mounted inside your hearing aids, which act personalized, wireless loudspeakers. When used with devices mentioned above, T-coils help block out the frustrating background noise so you only hear what comes through the device you are listening to such as the TV, audio/MP3 player, etc. One technology gaining acceptance throughout the U.S. is the induction loop. An induction loop simply creates a magnetic field which is picked up by the T-coil, allowing T-coil users the ability to hear in church, auditoriums, meeting rooms, etc. with only their T-coil turned on. This technology negates the need for headphones typically provided in these environments and users rave about the quality of the sound. 
It is estimated that about 70-80 percent of hearing aids in the U.S. have T-coils. Most of the newer hearing aids are being equipped with T-coils. However, the very small hearing aids that go all the way in the canal do not typically have room for the T-coil, although technology for smaller T-coils is catching up and it is expected that these will one day be able to accommodate T-coils. Certainly demand will play a part in this technology. Bluetooth technology is being installed in some new hearing aids. The Bluetooth technology is short range and is great for telephone and TV but still does not offer help in larger venues. Some Bluetooth streamers have a t-coil and will work in the loop.
Many people do not know if their hearing aids have T-coils. Check with your audiologist to make sure they are installed, activated and set for your personal needs. We find that many t-coils are set too low and need to be adjusted to a higher volume, or the orientation of the coil needs to be changed to get the full benefit from the hearing loop. It is important to have a manual button for the t-coil. Most Auto-coils will not be activated by the loop so be sure you ask for a MANUAL T-coil setting. Another popular option is an MT setting which allows a small amount of the hearing aid’s microphone in the mix so room sounds such as someone speaking next to you can be heard. These are personal choices which the audiologist can help with.
NOTE: Cochlear brand implants do not currently have a vertical t-coil which affects the experience in the loop. However, Cochlear has come out with a Loop Booster accessory to help their clients hear better in looped venues.