GB745724A - Improvements in alarm mechanisms - Google Patents

Abstract

745,724. Theft alarms. LARSEN, F. P. Oct. 30, 1951 [Dec. 18, 1950], No. 25366/51. Class 118(1) An alarm device comprises a box containing a rod 2 which, when the device is set, is capable of vertical motion and to the lower end of which is attached a weight 9 normally resting on the surface on which the box is supported, the weight being so attached to the rod 2 (i.e. by a ring 8 passing through a small hole 7), that on moving the box the weight is displaced and the rod is free to move'downwards under the action of a spring 10 thus operating an alarm, e.g. by closure of contacts 13. The box may be used either as a safe or locker or as a safety device which may be located at a suitable point such as by a door or window or over a stack of documents to. be protected. As shown in Fig. 1 the device is inoperative, and it is set by the rotation of a key 19 through a right-angle, the key being removed through key-hole 19b. This causes the locking member 16 to move to the left, thus disengaging a wedge-shaped member 21 from an extension 22 of the rod 2 and also bringing up a flexible member 16a which bears against the end of the contacts 13 and is deformed in doing so. Upon disturbance of the box so that the weight 9 moves to one side and .the rod 2 falls, the depression of the contacts 13 by the arm 12, allows the member 16a to straighten and prevent the contacts 13 from being opened even if the rod 2 is restored to its original position. In a modification (Fig. 5, not shown), motion of the member 2 operates through rack-and-pinion gearing upon a movable member having a tumbler action and acting upon the contacts 13. In a further modification (Fig. 6, not shown), downward movement of the rod 2 releases a spring-loaded . member to cause the subsequent closure of the contacts 13. The electric-alarm illustrated may be replaced by a clockwork mechanism.