SECURITY ALARM SYSTEMS

Abstract: A security alarm system includes a main alarm system (11), a main audible warning device (12) connected to said main alarm system, an auxiliary audible warning device (20) and a control means (23, 24) sensitive to disconnection of the main alarm circuit for operating the auxiliary audible warning device The auxiliary audible warning device, the control means and an auxiliary battery (22) are contained in a housing (21) and a wire connects the control means to a supply terminal of the main alarm system (11) such that the auxiliary audible warning means is energised by the auxiliary battery if this wire is severed.

Description: SECURITY.ALARMSYSTEMS This invention relates to secur y alarm systems, and has particular, but not exclusive, application -co vehicle theft alarm systems. Background Art It has already been proposed to provide an alarm system which, when armed, detects various signals es lt n from an intruder opening doors, or, in a vehicle system, switching on the vehicle ignition or other accessories or tampering 1 with the wiring 1 of the vehicle. Such systems suffer from the disadvantage, however, that -hey can be silenced merely by disconnecting the horn, siren or Q.ι sr audible alarm device, or disconnecting e alarm circui from the vehicle battery. It is an object of the present invention to provide a security alarm system in which this disadvantage is obviated. Disclosure of invention A security alarm system in accordance with the invention comprises a main alarm circuit, a main audible warning device operable under the control of said main alarm circuit, an auxiliary audible warning device and control means sensitive to disconnection of the main alarm circuit for operating said auxiliary audible warning device. Preferably the auxiliary audible warning device, the ' control means, and an auxiliary battery for auάible warning device are contained in a housing and are connected to the main alarm circuit by a wire, the control means being such that the auxiliary audible warning device is ooerated if such wire is severed. BAD ORIGINAL f OMPΓ In a vehicle system, the auxiliary battery may be connected to the vehicle main battery via a relay which is controlled by the vehicle ignition switch so that the auxiliary battery is maintained charged w en the ignition switch is closed, but is isolated therefrom when the ignition is off, thereby preventing discharge of the main battery by the auxiliary audible warning device. The control means preferably comprises a first relay having its winding- connected to the supply terminal of the main alarm circuit, and a second relay controlled by a contact of the first relay and controlling connection of the auxiliary audible warning device across the auxiliary battery, the two relays being normaiiy energised by virtue of their connection to the main alarm circuit. 3rief description of drawings An example of the invention is shown in the accompanying drawing which is a schematic circuit diagram of the alarm system, as applied to a vehicle theft alarm system. 3est mode of carrying out the invention A main alarm circuit 10 is contained within an enclosure 11 and has connections which are known per se to a key-switch 12, a series of trip-switches or vibration sensitive switches 13, to a contact of the vehicle ignition switch 1^, to the vehicle battery 15 and the vehicle earth and to a main audible warning device io. The circuit 10 (when armed) operates in a manner also known per se to detect closing' of any of the switches 13 or by so-called earth-drop detection: the energisation of any vehicle load and to sound the device l for a period following such detection. 3y using earth-drop detection, the circuit may be made sufficiently sensitive to detect the connection of any additional load to the vehicle BAD ORIGINAL electrical system. Various delays are provided to enable the driver to leave the vehicle after arming the circuit and to disarm the circuit after entering the vehicle, the latter such delay being overridden by the key-switch 12. Since all these basic functions of the alarm circuit are known in the art no detailed description of the main alarm circuit zxβ&d be given herein. The system shewn in the drawing also includes an auxiliary audible • warning' device 20 contained in a separate enclosure 21 which also, houses an auxiliary batter 22 and two relays 23, controlling the auxiliary audible warning 1 device 20. One such relay 3 has a single normally closed contact and has one end of its winri- 1- r, ~- connected by a wire 23 to the main battery input to the main alarm circuit 10, such wire being connected to the circuit 10 inside the enclosure 11. The other end of the winding of relay 23 is connected to the earthed terminal of the main warning device 16. A fuse 2β inside the enclosure 21 connects the wire 5 to the winding of relay . The winding of relay 2k is connected between the fuse 2β and the vehicle earth- The contact 3a is connected in series with a manual switch 2 across the winding 2k and the normally closed contact 2^a of relay 2k connects one terminal of the device 20 to the auxiliary battery ÷ve terminal, the other terminal of the device 20 and the -ve terminal of battery 22 being connected to the vehicle earth. Both relays 23 and 2k are normally energised so that contacts 3 and ^a are open. Contact 23 closes if relay 23 is d-a—energised by disconnection of the nain warning device lo from earth or by disconnection of the main supply lead to the main alarm'. In either case relay 2k is also de-energised causing the device 20 to be connected across the auxiliary battery 22. It will be noted that if the wire 25 is disconnected or if either terminal of the main vehicle battery 15 is disconnected BAD ORIGINAL rail 23 will be de-energised- If these connections are now re-established the fuse 26 will blow since, contact 23a and switch 2? in series provide a short circuit to earth- The fuse 26 will also blow if * the earth connection of the device l6 is severed- Zn either case resetting of the auxiliary alarm can only be effected by opening switch 27 and then replacing the fuse 2 . To maintain the battery 22 charged, there is provided an additional relay JQ which has its winding' connected between the vehicle ignition switch and the vehicle earth so that relay 30 s energised whenever the ignition is on. The normally open contact of the relay interconnects the positive terminals of the two batteries so that these are in parallel when the ignition is on, but isolated from one another when the ignition is off. Setting off of the auxiliary warning device 21 will thus not drain the main battery when the ignition is off. AJLthough an example of the invention has been described above as applied to a vehicle theft alarm system, the invention can also be applied to intruder alarm systems for boats, caravans, houses and other property. Ai hough. "earth-drop - detector systems are preferred, the invention may also be applied to system in which the main alarm circuit makes use of other methods of detection. Xn a modification of the system described above the end of relay 2k shown earthed, is connected by a fly lead to a radio or any other accessory in the vehicle which requires protection against theft, such accessory providing the connection of this fly lead to earth. Removal of the fly lead or disconnection of the accessory will cause de-energisation of relay ^- so that warning device 1 is oOerated. ^^AD l^^ 1 ' " Where there are two accessories which require independent protection, the lead from the relay 23 to the warning device lβ may be connected to a second earthed accessory instead of to the warning device io. Dis¬ connection of this second earthed accessory would likewise cause device 21 to be energised. BAD ORIGINAL CM?I

Claims: Claims : 1. A security alarm system comprising a main alarm system, a main audible warning device operable under the control of said main alarm circuit, an auxiliary audible warning device and control means sensitive to- disconnec¬ tion of the main alarm circuit for operating said auxiliary audible warning device. 2. A system as claimed in Claim 1 in which the auxiliary audible warning device, the control means, and an auxiliary baitery for the auxiliary audible warning device are contained .in a housing and are connected to the main alarm circuit by a wire, the control means being such that the auxiliary audible warning device is operated if such wire is severed. 3. A system as claimed in Claim 2 forming par"t of a vehicular system in a vehicle h ing a m i battery and an ignition switch, the auxiliary battery being connected to the main battery via a relay which is controlled by the vehicle ignition switch so that the auxiliary battery is maintained charged when the ignition switch is closed, but is isolated therefrom when the ignition is off, thereby preventing discharge of the main battery by the auxiliary audib1e -warning' device. +. A system as claimed in any preceding claim in which said control means comprises a first, relay having its winding connected to the supply terminal of the main alarm circuit and a second relay controlled by a contact of the first relay and contr-oliing connection of the auxiliary audible warning device across the auxiliary battery, the two relays being normally energised by virtue of their connection to the main alarm circuit. ~ . A system as claimed in Claim k in which said first relay wiring is connected between the supply terminal of the main alarm circuit and a grounded terrainal of the audiliary audible warning device. β. A system as claimed in Claim k in which the first relay winding is connected between the supply terminal of the main alarm circuit and an accessory device vhzzlah. is grounded. 7. A system as claimed in Claim 5 or Claim 6 in which " the second relay winding ' is connected between the supply terminal of the main alarm system and ground via a fuse, the first relay having' a normally open contact connected i- paraj.lal with said second relay winding whereby the first is blown when the first relay is de-energised. 3. A system as claimed in Claim 7 in which said second relay winding 1 is earthed via a wire connected to an accessory device so that the auxiliary audible warning device is energised, if said accessory device is dis¬ connected from- earth.

Inventors: NIPPER JOHN
Applicants: NIPPER JOHN
Application year: 1981
Main classification: G08B29
IPC codes: B60R25, G08B29