Abstract: The device for the contactless measurement of the rotational speed of a first part which rotates during operation and which is arranged inside a second part that either does not rotate or rotates at a rotational speed that is independent of the rotational speed of the first part, has an arrangement which generates a magnetic field and a magnetic field detector, wherein the arrangement which generates the magnetic field has a magnet ring (4) integrated in the inner part (1) and wherein the magnetic field detector is a Hall-effect sensor (3) situated in a housing (6) that surrounds both parts: the second part (2) consists of a non-magnetizable material.

Abstract: Parking brake, notably for automatic transmissions of motor vehicles, which is released via hydraulic pressure acting on a spring accumulator (3) and which is additionally held in the released state by a locking system (13) is actuated by a magnet (5) through which a current flows. The locking system (13) is kept activated and thus the parking brake released until the magnet (5) in the position in which the locking system (13) is actuated, has a power consumption lower than necessary for loading the locking system (13).