A locking device and system are disclosed. The locking device includes a barrel within which sets a plug. A plurality of pins sit in pin pathways that extend partially through the barrel and plug and the pins prevent rotation of the barrel within the plug when the ends of the pins are not aligned with a shear line. One of the pins has a recess formed therein within which a locking ball can sit. The engagement or otherwise of the locking ball in the recess is controlled by a linear actuator. When the linear actuator allows the locking ball to disengage the recess the pin with the recess in can engage the key and a line the end of the pin with the shear line.