Abstract: A system for securing the loading doors of trucks, semi-trailers, and other like enclosures against forced or unauthorized entry should the usual manually operable closure device on such doors be breached. The system comprises a locking arrangement which is disposed entirely within but which is selectively operable from the exterior of the enclosure as by a special key or by activation of an electronic or electric circuit through entry of a predetermined code or signal. The locking arrangement includes a plunger which is automatically engageable with a strike member to secure a door upon its closure and which is moveable to an inoperative position by the action of a pneumatic or hydraulic cylinder or electric solenoid or other like activator.