A motion sensor, and an implantable cardiac stimulator incorporating such
a motion sensor, has a fluid-type housing containing a fluid that
includes at least one type of anisotropic molecules, the anisotropic
molecules exhibiting an anisotropic property having a state that changes
dependent on motion. The housing of the motion sensor is located
externally on an animate subject, or is implanted in the animate subject,
and includes externally accessible electrodes that detect a change in the
state of the anisotropic property and emit an output signal
representative of an activity level of the subject.