I've had success with Williams Sound neckloops, also Comtek and Phonic Ear. I am not sure the latter two are even made anymore. None of these have batteries or controls, they are simply plug in and turn your telecoils on; hearing aids and/or CIs. Other brands have batteries that allow you to control the volume and get more power. I have manual volume control on my personal devices, so find those models unnecessary. And, I don't have to have batteries handy if they die. Others may tell you they like the options that come with the powered neckloops. Not me.