Abstract: A security device adapted to be applied to retain in closed relation container doors for lading against access into the container. The security device has a shelf portion with an upright arm secured thereto and adapted to be disposed in the path of opening movement of one or both of the container doors to prevent opening movement of the doors sufficiently to gain access to the lading in the container. The arm may be a part of an upright angle bar which forms a support for one end portion of the shelf portion while the opposite end of the shelf portion is supported by a rear upright member. The shelf portion is preferably yieldable to accommodate containers supported in different positions with respect to the surface of the transport vehicle. The upright arm may have a laterally extending arm connected therewith whereby the security device will have a retaining device in the path of both doors. Provision is made for discouraging cutting of the upright arm so as to remove it from the path of the door.

Abstract: A container monitoring system has a small transmitter unit adapted for easy attachment to and removal from a container such as a truck, trailer or railroad car when not in motion and a receiver which alerts a guard as to a theft-related movement either of the container itself or motion into or out of the container, or to a condition within the container such as temperature. The apparatus has provision for transmitting a low power, radio frequency carrier signal, preferably 27 MHz with a wire loop which is mounted to utilize the metallic body of the container as part of the antenna radiation system. The carrier is modulated with a mid-frequency signal that is interrupted at a precisely controlled low frequency rate and has a signal duration of a predetermined different inerval as measured from the theft-related movement.