The Machinery Backing-up Alarm is either a siren or a strobe light mounted on the back or roof of a tractor or other piece of equipment to warn people with low vision, low hearing, or slow reflexes that the machine is moving in reverse. On-road vehicles already have reverse lights, so the alarm can be wired into that same circuit and will sound or flash whenever the vehicle backs up. For machinery that does not have such circuits, a switch must be mounted to turn on the alarm whenever it is backing.