Lock assembly

A lock assembly comprises a lock cylinder having keyway 11 for operating a locking member 51. A lock cylinder shield 20 is moveable, e.g. sliding, from a first position which partially obscures the keyway to prevent insertion of key to a second position which exposes the keyway and permits insertion of a key. In the second position the shield actuates an engagement means 30 preventing rotation of the lock cylinder. The lock cylinder may include a plurality of disc detainer plates 54 with true gate (56, fig.3) for location of side bar (52) and may include a radial groove (57) for abutment with engagement plate 31 of mechanism 30 when shield in second position; engagement plate 31 moved shield 20 via lever 32. Preferably lock includes pin shield (80, fig.7) and vibration generator (91, fig.7) to generate vibrational noise during picking attempt. Also claimed is a key with a gap or notch in the stem to permit rotation of key in shield. Alternatively key could be inserted into lock and shield encompasses an integral/captive key head (71, fig.10)