1. Apparatus comprising in combination: (a) a sensor for taking measurements of light that has traveled from an illumination source, then to a diffusely reflective surface, then to a moving object, then to the diffusely reflective surface, and then to the sensor, such that the measurements are taken when the moving object is moving relative to the sensor and to the illumination source and is visible to neither the sensor nor the illumination source; (b) the illumination source for emitting the light; and (c) one or more processors for calculating, based at least in part on the measurements, motion or size of the moving object; wherein the sensor includes a phased array.