A telecoil is a very small copper wire built into a hearing aid. Having a telecoil in your hearing aids gives you the option of hearing significantly better in places that have a hearing loop, an FM system or an IR (Infra-Red) system. The telecoil works as an antenna to pick up magnetic signals and streams them as sound into your hearing aids. A hearing device with telecoil is a smidgeon bigger than a hearing device without telecoil but can add to the life of the battery even if not used on a regular basis.