The present disclosure includes a retrofit sensor module for use with a protective head top with a helmet and a visor. The sensor module includes a sensor housing and an attachment mechanism. The sensor housing encloses a head presence sensor to sense when the protective head top is being worn. The sensor housing also encloses a position sensor to sense the position of the visor relative to the helmet. The retrofit sensor module further comprises an attachment mechanism secured to the housing. The attachment mechanism mates with a first hinge component of a hinge assembly in the protective head top to removably install the sensor module into the protective head top, wherein the hinge assembly allows the visor to move relative to the helmet.