A vestibular prosthesis system is described which includes an external movement sensor that is attachable a patient's head for generating an external movement signal. An internal movement sensor is implantable under the skin of the patient's head for generating an internal movement signal. A fail-safe sensor is configured to detect movement of the one or more external movement sensors relative to the head and generate a corresponding relative motion signal. And an implant processor also is implantable under the skin and in communication with the internal movement sensor and the external transmitter for generating an implant stimulation signal based on one of the movement signals and/or the relative motion signal to electrically stimulate target neural tissue for vestibular sensation by the patient.
