A sensor assembly for a passenger conveying device, a safety system and the passenger conveying device, wherein the sensor assembly comprises an optical fiber disposed along a length of a skirt board of the passenger conveying device; a light source disposed at a first end of the optical fiber, light being incident into the optical fiber; and an optical receiver disposed at the first end of the optical fiber, the optical receiver receiving backwards scattered light from the optical fiber and being capable of sensing a signal indication of the backwards scattered light, wherein the optical fiber is associated with a sensing element such that the sensing element causes deformation of the optical fiber when the sensing element is subjected to pressure, and the optical receiver is capable of sensing a change in the signal indication of the backward scattered light caused by the deformation of the optical fiber.