They use a computer to adjust mine up or down, I’m low Freq loss due to botched Inner Ear Perfusion by a SADISTIC SOB ENT. Nor do they solve all hearing problems, run water or be in another room, turn up the TV to much and you over drive them just like loud speakers do when in the grocery store, if you go to the movies, mall, shopping, you have to remove them or you’d go nuts trying to survive the over drive, and you can’t turn them down enough to compensate. Let the wax trap get to full and you don’t hear. That word Battery in you ear is a pain in the tush as it is to loud and you have 1 min to change the battery or less depending on brand of aid.
Considering the cost why not make them rechargeable?