The outer hair cell (OHC) possesses a nonlinear charge movement whose characteristics indicate that it represents the voltage sensor responsible for OHC mechanical activity. OHC mechanical activity is known to exist along a restricted extent of the cell's length. We have used a simultaneous partitioning microchamber and whole cell voltage clamp technique to electrically isolate sections of the OHC membrane and find that the nonlinear charge movement is also restricted along the cell's length. Apical and basal portions of the OHC are devoid of voltage sensors, corresponding to regions of the cell where the subsurface cisternae and/or the mechanical responses are absent. We conclude that the physical domain of the motility voltage sensor corresponds to that of the mechanical effector and speculate that sensor and effector reside within one intra membranous molecular species, perhaps an evolved nonconducting or poorly conducting voltage-dependent ion channel.