silent piano for practicing
• (n.) A small dumb keyboard used by pianists for exercising the fingers; -- called also dumb piano.
Dig`i·to'ri·um noun [ New Latin , from Latin digitus a finger.] A small dumb keyboard used by pianists for exercising the fingers; -- called also dumb piano . 
A digitorium is a small portable dumb instrument having a short keyboard with five keys like those of a piano, formerly used by piano-players for practice, to give strength and flexibility to the fingers.
digitorium A small dumb keyboard used by pianists for exercising the fingers.