My 1923 Steck upright pianola has a lever which locks the keys.
However, when the lock is 'off', the keys do not move because of
the way they are balanced.

Barrie Land

 [ That's true of the British Steck Pianola, but the keys of the
 [ American Steck Pianola are balanced so that they _will_ move when
 [ the player is operating.  The American Steck is provisioned with
 [ a key lock device (actually a wedge) operated by a hand-lever
 [ beneath the keybed below the treble keys.  -- Robbie