Many people will struggle to read this article in print or on a phone or tablet because their hands are shaking. They also may find it hard to eat, dress, work and do other things that the rest of us take for granted. Most of them do not have a well-known brain disease such as Parkinson’s. Instead, they have what doctors call “essential tremor.”

This illness, the most common movement disorder, affects seven million Americans, most of them elderly. New devices such as high-tech eating utensils can compensate for the tremor...