Locking Unit

A locking unit for the parking brake of an automatic transmission, for locking the movement of a piston which can be moved by a drive, wherein a guiding element presses catch elements radially outward and a magnetic element for sensing the position of the guiding element is connected to the guiding element. A locking device for the parking brake of an automatic transmission, wherein a piston is locked with catch elements which are guided by a guiding element which in two end positions presses different catch elements radially outwardly in each case for locking.