A method and apparatus for monitoring the security of closures of the type used on large trucks, and shipping or other containers wherein one or more doors are provided on an end and/or the sides of the container and are secured by vertical rods having cam-like latches at their ends that are rotatable from a first disposition in which they engage keepers to lock the doors in a closed position, and a second disposition in which they disengage the keepers to unlock the doors and allow them to swing into an open position. More specifically, the present invention relates to a monitoring assembly that attaches between the locking rod handles of the containers, senses any movement of the locking handles or the opening of the doors, and provides visual signals and/or transmitted signals as an indication of tampering.