Abstract: An improvement in a locking device of the type having a series of reference combinations arranged serially upon a tape. A combination is entered into the system by a set of push buttons. The combination entered is compared with the reference combination. If both combinations are complementary, the system can be unlocked. The improvement prevents the unauthorized ascertainment of the combination needed to release the device. An isolation or restraining bar acts as a buffer between an internal gate and a set of tumbler levers. When an actuator knob is turned to unlock the system, the tumbler levers normally will engage with the gate when the combination push buttons are not set to the proper combination. The combination then becomes ascertainable, because the tumbler levers that require actuation, transmit movement to the push buttons when contacted by the gate.