Every owner of a transport company knows that the most important, and therefore the most valuable part of a delivery vehicle is the trailer. After all, it is here that the transported goods are located. Cargo worth several, and sometimes even tens of thousands of Euro. No wonder that this type of transport is nowadays a tasty morsel for thieves. A moment of inattention or a stop in an unguarded parking lot is enough for a break-in. In that case, how to protect the trailer against theft? The best method is an appropriate, i.e. effective, locking of the trailer door.