Hi Group,  Jim Perkins asked about animated keys on an upright piano.
It is the weight of the keys that allows them to fall when the
whippens are lifted.  On my Gulbransen upright there is a felt covered
bar hinged to the keyed under the fronts of the keys.  It is attached
to a key slip lever which is labeled "Key lock."

When the lever is pushed to the right the felt covered bar is lifted
to the underside of the key fronts so that they are resting on the felt
and remain motionless when the whippens are lifted and are unplayable
by hand.

Jack M. Conway, Los Angeles, California, USA