Patent GB-637231-A (GB)
Title: Burglar and like alarms
IPC: H01H3/16
Filed: 1946-08-29
Abstract: 637,231. Burglar and like alarms. BRIOT, P. Aug. 29, 1946, Nos. 26039 and 26040. Convention dates, April 2, 1943 and Jan. 17, 1944. [Class 118 (i)] A burglar alarm apparatus which comprises an auxiliary bolt controlled by the normal lock of a door and a security device fixed to the inside of the door-frame is characterized in that the said security device comprises a casing containing a resilient contact member held in its non-operative position by a catch and arranged to be released when the auxiliary bolt is displaced by an opening movement of the door to operate an alarm. The means for securing the security device to the door-frame are so arranged and located with respect to the contact member that when the alarm has been operated, by an attempt to open the door without unlocking it, it can be silenced only by forcing the auxiliary bolt out of engagement with the security device by opening the door and then dismantling the security device. On the wall 17, Fig. 1, immediately above the door 18 to be protected is fitted a base-plate 1 to which is bolted a cover 2. Mounted on the door is a bolt 19 which may be operated from outside the closed door to project through a slot 8 in the cover 2. If now the door is moved inwards the bolt 19 releases a spring contact member 6 from a retaining lug 10, the member 6 springing upward to close contacts 7, 11 and energize an electromagnetic horn 3. Continued movement of the door 18 causes the bolt 19 firstly to break a glass container 12 of a smoke generator and then finally abut against the edge 21 of the slot 8. The cover 2 is secured to the base-plate 1 by means of a long hollow screw 13 and a nut 14. In order to tamper with the alarm mechanism it is necessary to unscrew and remove this screw 13 and this can only readily be done by inserting therein a special tool which will pass medial projections in the hollow screw 13 and engage with a lug at the nut end, and this tool can only be inserted when the door is open. In a modification, Fig. 4, the contact member 6 may be latched beneath the corner of the base-plate 1 by depressing a projection 22 extending through a slot in the mounting plate 4. The release of the member 6 by slight movement of the door (due e.g. to wind) is prevented by the interposition of a suitably resistive member 23 between the bolt 19 and the contact member 6, which member 23 must be broken before the alarm is sounded. The battery and audible alarm 3 may be tested by pressing an earthed spring contact 25, through an aperture 28 in the casing 2, against an insulated contact 27 and hence earthing contact 11. The hollow fixing screws 13 slope inwards toward the door to prevent their removal when the door is closed. When more than one entrance is to be protected, a device as described above is fitted to the main door and the shooting of the bolt 19 thereof closes an auxiliary contact 30, Figs. 6, in series with each of the subsidiary sets of contacts 35 which are situated at each subsidiary entrance to be protected and are closed by known means when forcible entry is attempted. After the contacts 30 are closed the closure of contacts 35 will energize a relay 31 whose contacts 32, 33 operate the audible warning device 3 and whose contacts 32, 34 close a holding circuit. The main contacts 36 are operated by the auxiliary bolt on the main door as previously described.