A weight sensor comprising a weighing platform and a load cell coupled to the platform to sense a weight applied to the platform, the load cell comprising a deformable plate with one or more strain gauges arranged to provide an electrical signal representing the weight applied to the platform, and a base supporting the load cell, wherein the deformable plate is movably mounted to the base at only three contact points, the contact points allowing lateral movement of the plate relative to the base when the plate deforms in response to a weight applied to the platform. The weight sensor makes it possible to independently monitor the weight and weight shifting of two people sharing the same bed. The weight sensor is selfcentring when a load is applied off-centre to the platform, which is particularly beneficial when such a weight sensor is used underneath a bed, e.g. under a bed leg or other support member which may not be aligned centrally over the weight sensor. Beneficially the sensor is not unduly affected by minor misalignment of the leg of a bed relative to the load cell.
