A thief-trapping apparatus for a room having a closure permitting room ingress and egress and an object therein to be safeguarded utilizes a locking mechanism for the room closure and a cord having a frangible link. The locking mechanism includes a bolt and a bolt receptacle which are operatively mountable on the closure and the wall of the room adjacent the closure. When operatively mounted on the room wall and closure, the bolt is movable between a first position at which the bolt cooperates with the bolt receptacle to lock the closure in a closed condition and a second position at which the closure is unlocked. The locking mechanism further includes a spring for biasing the bolt from its second position to its first position, and the cord is fastened at one end to the bolt so that when the cord is pulled from its other end, the bolt moves to its second position. The other end of the cord is fastenable to the room object to be safeguarded so that if, after the other cord end is fastened to the room object so as to hold the bolt in its second position, the bolt is disconnected from the object by the occurrence of an event, such as the breaking of the frangible link in the cord, the bolt is moved by the spring to its first, or closure-locking, position.