Abstract: Thin, planar sensors for measuring forces exerted by mattresses or chair pads on a patient's body include a central conductive elastomeric pad movable in a horizontal plane into more or less intimate contact with flexible peripheral conductors adjacent the central pad, thus varying electrical conductivity between the central pad and peripheral conductors by a surface piezoresistive effect proportional to the magnitude and direction of horizontal shear forces exerted on the pad. The preferred embodiment comprises a matrix area array of thin, square central conductive elastomeric pads, each surrounded by four square peripheral conductive elastomeric pads forming a close pack tiling arrangement that utilizes inner peripheral conductors in the array to function as one of the peripheral conductors for two or three nearest-neighbor sensors.