Abstract: A locking unit for a passenger restraint device of an amusement ride passenger unit has a cylinder-piston unit with a piston rod, a hydraulic accumulator and an electronic unit. The electronic unit has a sensor unit for monitoring the position of the piston rod. The electronic unit can be switched to a first measuring mode, wherein the piston rod is at least partially retracted. In the first measuring mode, the electronic unit detects actual positions of the piston rod over a first reference period by means of the sensor unit and compares them with a first limit position range stored in the electronic unit, the electronic unit generating a warning signal in the event of a deviation between the actual positions and the first limit position range. Furthermore, an amusement ride passenger unit includes such a locking unit and a method allows for functional testing of such a locking unit.