1,165,989. Anti-theft locks. SAM SHIAOMING HSU. 24 June, 1968, No. 29973/68. Heading E2A. An anti-theft arrangement associated with a conventional lock, such as a cylinder lock 23, prevents operation of the lock when the correct key is inserted, unless a predetermined number on a dial 25 has previously been set against a pointer carried by the lock casing 21, by causing a spring-loaded pin 42 slidable in the casing to be blocked by a trapping ring 36 which is rotated through gearing 29, 38, 37 by the dial, a rod 45 projecting from the pin 42 being trapped within the U section of the trapping ring unless the latter is disposed with a slit (35, Fig. 3A, not shown) in register with the rod, the pin 42 when blocked arresting movement of an arm 46 rotatable with the lock barrel so that only a small amount of lock movement has occurred, insufficient to open the lock. Before engaging the pin 42, the arm 46 releases another spring-loaded pin 51 which causes a rod 52 carried by this pin to engage between adjacent teeth 53 of a series of such teeth extending around the trapping ring so preventing movement of the dial and at the same time preventing return of the arm 46, so that when the pin 42 is in blocking condition the arm 46 is jammed between the two pins and the key cannot be withdrawn from the lock. When, however, the correct number has been set on the dial 25, the arm 46 is able to ride over the rounded end 44 of the pin 42 and complete a full circle movement to open the lock. At the end of this movement a projection. 56 on the arm 46 engages a flange 55 on a second arm 54 causing the latter also to ride over the pin 42 and come to rest against a stop 59. This enables the key to be rotated back into the locking position since the two pins 42 and 51 are interconnected by a lost-motion coupling 57, 58 and, on return of the arm 46, a further projection (60, Figs. 5 and 7, not shown) on the arm 46 picks up the second arm and pulls the latter over the pin 42, depressing the latter to an extent sufficient also to withdraw the pin 51 so that arm 46 can return fully and the key be withdrawn. The face of the pin 51 opposite to that engageable with the arm 46 (to prevent its return when the number set was incorrect) is chamfered so that arm 46 can ride over pin 51 when moving to the fully unlocked position in normal operation (with the correct number set on the dial). In order to remove a key which has been manipulated in the lock with the incorrect number set on the dial it is necessary to follow the following procedure: first, 32 which carries the gears 29, 38 is slid axially, by pushing in the dial 25, to disengage gear 38, this being possible only when a key is partially turned to release the pin 51 (The opening number may incidentally be changed by doing this, rotating the dial and re-engaging the gears); it is then necessary to manipulate a further combination lock mechanism which is totally enclosed within a casing 80 on the inside of the door 22 to which the lock is fitted, this lock mechanism consisting of five levers 73 each of which can be picked up in turn by a setting lever 78 secured to the shaft 32, when the latter is slid axially as above, since a plate 71, mounted on splines 69 so as to be non-rotatable, and carrying the setting levers, is coupled to the shaft so as to move axially with the shaft, the levers being then set to a known combination by rotation of the dial by the authorised user, who alone knows this combination, whereby pins 74 carried by the respective levers can be positioned opposite corresponding bores 68 in the door to allow axial movement of shaft 32 in the opposite direction, i.e. outwardly, which causes coupling 64 to be moved sufficiently to withdraw both pins 42 and 51 to release the jammed arm 46.