following description taken in connection with the accompanying drawings in which fig1 is an elevation of the rear of a code combination lock and key for a safety deposit or strong box the device being shown in blocking position fig2 illustrates in plan view a slidable control element used in the device shown in fig1 fig3 illustrates in plan view the blocking lever used in the device shown in fig1 fig4 is a view similar to fig1 but showing the parts for unauthorized attempt to open the lock without preparatory energization of the electromagnetic device fig5 shows a top view of the device in fig1 but in open position fig6 illustrates a front view of a lock for a safety deposit box for a bank in blocked and locked position fig7 illustrates the lock shown in fig6 but in open position fig8 illustrates the same device pursuant to an attempt to opening without preparatory electromagnetic energization fig9 a b and c are plan views of several individual parts used in the device shown in fig6 8 fig1 is a partial internal view of the device shown in fig6 fig1 is the rear view of a safety deposit box with the lock shown in fig6 10 but on a smaller scale fig1 is a front view of another safety deposit box and fig1 is a rear view of the safety deposit box shown in fig1 proceeding now to the detailed description of the drawings fig1 illustrates the rear side of a lock and key.