GB1261182A - Intruder alarm system - Google Patents

Abstract

1,261,182. Burglar alarms. A. SADLER. 17 March, 1969 [15 Dec., 1967], No. 52105/67. Heading G4N. A burglar alarm system comprises a master warning circuit arranged to produce a first alarm and an ancillary circuit arranged to produce a second alarm in response to operation of the master warning circuit and provision for the first alarm to be operated when the second alarm is operated by other means. When one of the detectors 5, 6 becomes open circuited by action of an intruder, transistor 22 becomes non- conductive after a time delay 25 so as to trigger a silicon controlled rectifier 34 which, after a further time delay 35 triggers a further rectifier 40 which turns on transistors 48, 53, energizing relay 52 and operating an alarm bell 54. Contacts 52/1 are coupled via conductors C1, C2 to an ancillary warning circuit (Fig. 2, not shown) in neighbouring premises whilst conductors D1, D2 couple contacts 52/1 to an external warning circuit (Fig. 3, not shown). The ancillary warning circuits are similar to that shown in Fig. 1 but omitting time delays. Operation of either ancillary warning circuit e.g. by the cutting of conductors C1 . . . D2 also actuates the master warning circuit shown. A further SCR is connected across the relay winding in the external warning circuit (Fig. 3, not shown) which may be turned on so as to silence the external bell. If the alarm in neighbouring premises is switched off, the master alarm bell 54 will operate unless the switch 80 is closed. The time delay enables an authorized person to enter or leave the premises without operating the alarm. Mode selection switch 56 prevents operation of either or both ancillary warning circuits. Intruder sensors.-The detectors 5, 6 may be switches operated mechanically or magnetically and may be moulded into a single block including a conductive loop 14, the cutting of which will operate the alarm. Resistors may be connected across each detector switch. A large inductance may be included in the control circuit, interruption of the current through which causes a large voltage to trigger the alarm. Alternatively, each detector may produce relaxation or other oscillation, the frequency of which is indicative of the location of the detector.