A limit sensor is fitted on the top and bottom of the stairlift rail. The limit sensors make sure that, when reaching the end of the rail at either end, the stairlift stops in the correct position. It also ensures that the stairlift comes to a soft stop. A smooth start stop motion is vital so as well as coming to a soft stop, the stairlift should have a slow, gentle start rather than a jerky start. This removes the risk of injury when the stairlift starts or stops. Curved Stairlifts are generally more expensive than the straight type because they have to be custom manufactured or specially adapted for the particular stairwell.