an electrical switch mechanism which operates in response to predetermined deceleration and / or acceleration is especially adapted for use on board trains for brake assurance purposes . switch contacts biased to a safe switching condition are actuated by an arm . a pendulum pivots a predetermined distance with respect to the vertical in response to a predetermined acceleration or deceleration . the arm is carried by the pendulum and may be mounted on a bracket plate such that the arm is set at a predetermined inclination with respect to the vertical . the arm actuates the switch contact only when the train reaches the predetermined acceleration or deceleration . the switch mechanism is vital in operation in that the safe switching state is maintained in the absence of actuation . by adjustment of the bracket and arm inclination , the mechanism can be set to respond to different selected accelerations and / or decelerations . two sets of contacts biased in opposite directions may be actuated by separate arms each carried by the pendulum . the mechanism is then responsive to deceleration in opposite directions and is especially useful in trains which run in opposite directions without turning around , such as subway trains .