Two lock systems are available. The "gravity lock" is equipped standard on the SlideMaster. It is a handle that unlocks the unit when it is turned either 90 degrees left or right and will locks the unit in both the seated and extended positions by rotation of a handle. The "spring lock" (HSL) is optional. Pulling on the handle releases for outward travel and pushing on the handle releases for the inward travel. The HSL automatically locks in the open and closed positions. There is an additional charge for the HSL option.