A mechanism, comprising: a primary system configured to undergo motion when a force is imposed on the primary system, the primary system comprising a rotatable disk rotatably movable about a central axis, and at least one further member linked to the rotatable disk, the at least one further member acting as a first motion characteristic sensor that senses at least two motion characteristics of the primary system; and a secondary system; wherein the primary system and secondary system are configured to remain kinematically independent of one another below a threshold of sensed motion characteristics, and, above the threshold of sensed motion characteristics, the at least one further member is configured to move to cause direct engagement between the primary system and the secondary system, thereby slowing or stopping independent kinematic motion between the primary system and the secondary system; wherein the at least one further member of the primary system comprises a pawl mounted on the rotatable disk on a pawl pivot axis for sensing primary system velocity and an inertial mass mounted on the rotatable disk for sensing primary system acceleration, the pawl and inertial mass being retained together by a pawl bias element, and a mass bias element being provided between the rotatable disk and the inertial mass, the primary system is configured to undergo motion according to a kinematic relationship when in use and a force is imposed on the rotatable disk, the pawl and the pawl bias element are configured to have a centrifugal force acting thereon when the rotatable disk spins, this centrifugal force acting against the pawl bias element, and the inertial mass being configured to rotate relative to the rotatable disk, against the mass bias element, on rotational acceleration of the rotatable disk, thereby moving the pawl bias element closer to the pawl pivot axis; and wherein the secondary system is kinematically independent to and surrounds at least part of the primary system, the secondary system comprising a latch member. a primary system configured to undergo motion when a force is imposed on the primary system, the primary system comprising a rotatable disk rotatably movable about a central axis, and at least one further member linked to the rotatable disk, the at least one further member acting as a first motion characteristic sensor that senses at least two motion characteristics of the primary system; and a secondary system; wherein the primary system and secondary system are configured to remain kinematically independent of one another below a threshold of sensed motion characteristics, and, above the threshold of sensed motion characteristics, the at least one further member is configured to move to cause direct engagement between the primary system and the secondary system, thereby slowing or stopping independent kinematic motion between the primary system and the secondary system; wherein the at least one further member of the primary system comprises a pawl mounted on the rotatable disk on a pawl pivot axis for sensing primary system velocity and an inertial mass mounted on the rotatable disk for sensing primary wherein the primary system and secondary system are configured to remain kinematically independent of one another below a threshold of sensed motion characteristics, and, above the threshold of sensed motion characteristics, the at least one further member is configured to move to cause direct engagement between the primary system and the secondary system, thereby slowing or stopping independent kinematic motion between the primary system and the secondary system; wherein the at least one further member of the primary system comprises a pawl mounted on the rotatable disk on a pawl pivot axis for sensing primary system velocity and an inertial mass mounted on the rotatable disk for sensing primary system acceleration, the pawl and inertial mass being retained together by a pawl bias element, and a mass bias element being provided between the rotatable disk and the inertial mass, the primary system is configured to undergo motion according to a kinematic relationship when in use and a force is imposed on the rotatable disk, the pawl and the pawl bias element are configured to have a centrifugal force acting thereon when the rotatable disk spins, this centrifugal force acting against the pawl bias element, and the inertial mass being configured to rotate relative to the rotatable disk, against the mass bias element, on rotational acceleration of the rotatable disk, thereby moving the pawl bias element closer to the pawl pivot axis; and wherein the secondary system is kinematically independent to and surrounds at least part of the primary system, the secondary system comprising a latch member.