GB2333627A

GB2333627A - Security system for windows

Info

Publication number: GB2333627A
Application number: GB9801446A
Authority: GB
Inventors: Brian Lawrence Birch
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-01-24
Filing date: 1998-01-24
Publication date: 1999-07-28
Anticipated expiration: 2018-01-24
Also published as: GB2333627B; GB9801446D0

Abstract

A motor vehicle (2) has a heating element (8) mounted on each and every window (4, 5, 6). A change over switch (14) in one position supplies the heating elements (8) with a heating current to effect demisting and in the other position supplies a sensor current. A monitoring switch (20) monitors the sensing current and activates an alarm (22) when the current changes in response to an attack on the windows.

Description

SECURITY SYSTEMS FOR WINDOWS The present invention relates to security systems for windows, in particular, but not exclusively, windows for motor vehicles.

Motor vehicles are being increasingly supplied with security devices. Such security devices usually have two functions. A first function is to disable the car when an unauthorised intruder gains access; while a second function is to activate the alarm when the car is tampered with by unauthorised personnel. These systems are normally activated in the absence of a driver but are deactivated when the driver occupies the car.

However, cars are increasingly becoming the subject of attack when a driver or passenger is present.

Such attacks may simply be for theft but can also be to harm the occupants, particularly if they are old, frail or of a particular gender. Sometimes, such attacks are the result of road rage incidents. While the occupant of the car can gain some protection by locking the car doors, he or she is still vulnerable where the attacker breaks one of the car windows.

It is an object of the invention to provide an improved security system.

According to the present invention there is provided a security system for a window having an electrically resistive element mounted on the surface of, or embedded in, the window, the system comprising first and second terminals for connection to the element, an alarm, control means for selectively feeding a heating current to the first and second terminals sufficient to enable demisting of the window when the resistive element is connected thereto, or a substantially lower sensor current, and means for monitoring the sensor current when supplied to the terminals, the monitoring means being responsive to a change in the sensor current as a result of damage to said element in response to the window being broken to activate the alarm.

Preferably, the change in current being monitored is an interruption of current. Instead, the change in current being monitored is a change in the resistance of the element.

Advantageously, each and every window of a motor vehicle has a window as described above coupled to the security system.

Preferably, the control means comprises a changeover switch for selectively feeding to the terminals a heating current to the sensor current supplied through the series combination of a current limiting resistor and a diode.

The monitoring means may monitor the voltage between the diode and the resistor. Preferably, the monitoring means comprises a voltage triggered semiconductor switch.

The alarm may be an audio alarm and/or a visual alarm.

A vehicle incorporating a security system embodying the present invention, will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side elevation of a motor vehicle; Figure 2 is a front elevation of one of the windows of the vehicle; and Figure 3 is a circuit diagram of the security system.

Most motor vehicles have a heated rear window in which a resistive wire is secured to the surface of or embedded in the glass of the window. The wire follows a sinuous path backwards and forwards across the window with successive traverses being spaced 0.5 to 1.0 cm apart to cover substantially the whole screen.

A switch is usually provided to supply a heating current to the wire which then warms the glass of the window to effect evaporation of any condensation.

In the car 2, shown in Figure 1, each and every window, the front windscreen 4, the rear window 5 and all the side windows 6, are provided with a resistive heating wire 8 (see Figure 2). In the event that any window is broken, the wire will also break.

The circuit shown in Figure 3 is arranged to selectively supply each of the windows 4, 5 and 6 with a heating current or a substantially lower, sensor current.

For the sake of convenience, only one heating wire 8 for one window is shown connected across terminals 10 and 12, although the other wires of other windows may be connected in parallel across the terminals 10 and 12.

As shown, a DC power supply 15 has one output connected to one terminal 10 and its other output connected to the other terminal 12 via a change over switch 14. In one position, the change over switch 14 feeds the terminal 12 directly while, in its other position, the change over switch feeds the terminal 12 via a resistor 16 and a diode 18 connected in series. The junction between the diode 18 and the resistor 16 is connected to the control input of a semiconductor switch 20. The output of the switch feeds an audio/visual alarm 22. Both the switch 20 and alarm 22 are powered from the power source 15.

In operation, with the change over switch 18 in its first position, the heating wire 8 is supplied with a heating current from the power source 15 and this effects demisting of the windows. When the change over switch is switched to its second position, either manually or automatically after a predetermined delay, the alarm system is activated. The current flowing through the heating wire 8 is substantially reduced by the action of resistor 16 to a very small fraction of its former value eg to 1/100th or to 1/1000th. The voltage appearing at the input to the switch 20 is thus substantially the same as that at terminal 10. If, however, the wire 8 is broken, the voltage at the input of the switch will rise to almost the full voltage of the power supply 14.

The switch 20 will accordingly trip to actuate the alarm 22. The alarm being activated, it would be hoped that the attacker would be frightened off or at least other passers by alerted.

A switch (not shown) may be provided to disable the alarm if and when required.

It will be appreciated that not only will the alarm act as a deterrent to attackers but it could also serve as a warning to other drivers in the event of a windscreen strike by a stone or the like.

While the resistive element has been described as a wire, it will be appreciated that it may comprise a transparent resistive layer forming at least part of the window and whose resistance changes when the window is broken. The change in resistance is then monitored to trigger the alarm.

Claims

CLAIMS 1. A security system for a window having an electrically resistive element mounted on the surface of, or embedded in, the window, the system comprising first and second terminals to which said element can be connected, an alarm, control means for selectively feeding a heating current to the first and second terminals sufficient to enable demisting of the window when the resistive element is connected thereto, or a substantially lower sensor current, and means for monitoring the sensor current when supplied to the terminals, the monitoring means being responsive to a change in the sensor current as a result of damage to said element in response to the window being broken to activate the alarm.
2. A system according to Claim 1, wherein the change in current being monitored is an interruption of current.
3. A system according to Claim 2, wherein the change in current being monitored is a change in the resistance of the element.
4. A system according to any preceding claim, wherein the control means comprises a changeover switch for selectively feeding a heating current to the element or a sensor current supplied through the series combination of a current limiting resistor and a diode.
5. A system according to Claim 4, wherein the monitoring means monitors the voltage between the diode and the resistor.
6. A system according to Claim 5, wherein monitoring means comprises a voltage triggered semiconductor switch.
7. A system according to any preceding claim, wherein the alarm comprises an audio alarm and/or a visual alarm.
8. A vehicle in which each and every window includes an electrically resistive element, incorporating a security system according to any preceding claim coupled to said elements.