A safety device for use in a fall arrest system, has a safety line drum mounted for rotation and a speed responsive engagement mechanism responsive to the speed of rotation of the drum, which is activated above a predetermined rotational speed of the drum to deploy an energy absorber. A rotational transmission member (which may be in the form of a shaft) is coupled, via the speed responsive engagement mechanism, when activated, to rotate with the drum. The energy absorber is deployed in response to operation of the rotational transmission member. The speed responsive engagement mechanism may be mounted intermediate the drum and the energy absorber for ease of replacement.