Abstract: A safety and security locking device is described for use with pneumatic brake air couplings to prevent access to the air coupling opening for applying air pressure to release the brake. First and second elongate arms are pivotally joined at a pivot access between the ends for pivoting motion between an open position and a clamping locking position. One arm is formed at one end with a flange or cover for covering engagement over the air coupling opening. A locking guide or projection extends from the flange within the perimeter of the flange and is inserted in the opening for guiding the flange or cover over the air coupling opening or other inlet orifice. The second arm is formed with a brace at the same end for engaging the air coupling or orifice on the opposite side from the opening in clamping opposition with the flange.