A weight sensor includes a pad of electrically insulative material having a through aperture and electrode plates secured to its top and bottom surfaces at least partially covering the aperture. An electrical contactor in the aperture responds to a compressive force applied across the pad thickness to electrically interconnect the electrodes and close a circuit that permits an alarm to be actuated. The sensor is disposed in footwear worn by a patient being rehabilitated from a lower limb surgery or injury. The stiffness/compressibility of the pad determines the applied patient weight or compressive force required to permit the contactor to close the circuit between the electrodes.