GB2289169A

GB2289169A - Printed circuit key for vehicle security

Info

Publication number: GB2289169A
Application number: GB9406795A
Authority: GB
Inventors: Francis David Harper-Jones
Original assignee: HARPER JONES FRANCIS DAVID
Current assignee: HARPER JONES FRANCIS DAVID
Priority date: 1994-04-06
Filing date: 1994-04-06
Publication date: 1995-11-08
Anticipated expiration: 2014-04-06
Also published as: GB2317421A; GB2317421B; GB9406795D0; GB9724749D0; GB2289169B

Abstract

A key is constituted by an electrical connector for making momentary contact with the pins 61 of a mating connector. The key comprises a printed circuit board 69 formed with plated through-holes 71 and is printed on its internal side with at least one track interconnecting a pair of the through-holes. The key may be used in a vehicle security system, in order to complete a circuit and actuate relay enabling the primary of an ignition coil. The relay is protected within a cover fixed to the top of the coil and receives input from the key via an electric or fibre optic link within an armoured duct. <IMAGE>

Description

Vehicle Security Device This invention relates to a vehicle security device.

A convenient way of immobilising a vehicle to prevent theft is to isolate the low tension ignition circuit in such a way that a thief cannot gain access to the wiring, thus preventing him from being able to reconnect the leads and so by-pass the isolating switch. This has been used previously on a vehicle immobiliser, where the two leads from the vehicle's electrical system to the low tension side of the ignition coil are removed and attached to new leads which are terminated inside a fixed plug which is conveniently mounted in the passenger compartment. Two additional wires, also terminated inside the fixed plug, are fed through an armoured flexible tube to the low tension terminals mounted on the top of the ignition coil. This flexible tube, which has a metallic grommet fitted to it at the ignition coil end, clips together with a special cover which is mounted over the top of the ignition coil. Such a cover is described in UK Patent No. GB2092388. The plug forms one part of a double-pole isolating switch. The second part of the isolating switch is a key which consists of a detachable socket which mates with the fixed plug and which has its contacts connected internally so as to complete the electric circuit to the ignition coil. The vehicle is immobilised by removing the key. The plug and key are multipin connectors having more than four pins and since only four wires are terminated on the plug they may be terminated to the pins in a number of different combinations, each one being unique and requiring a correctly wired key in order to operate the ignition circuit. A plug with ten pins is commonly used.

A disadvantage of this system is that the full low tension ignition coil current is taken to the fixed plug and back again. This can give a loss of electrical power along these leads. A large sized plug and key are required to carry this current and the key is a bulky item for the driver to carry around when the vehicle is immobilised. After many insertions the contacts become worn and power can also be lost at the contacts, causing the key to warm up. The leads which are not mounted inside the armoured tube can also radiate electrical interference.

I have now devised a vehicle security device which overcomes the disadvantages noted above, and which also provides improved security.

In accordance with this invention there is provided a vehicle security device which comprises a relay means operable to complete a circuit to the primary of an ignition coil, and a control line for the relay means extending to a remote key means which serves to actuate the relay means and complete said circuit.

The relay means (which may be of electronic or electromagnetic type) is preferably mounted adjacent the ignition coil, preferably in a housing or cover which fits to the top of the ignition coil. Preferably the control line comprises two or more electrical wires through which a circuit is completed, when the key means is actuated, to energise the relay means. Preferably the control line extends through an armoured cable or duct from the relay housing to the key means.

The control line may comprise a fibre optic link: in any event it may carry a unique digital code from the key means to the relay means.

In an embodiment which will be described herein, the security device or immobiliser uses a cover similar to the one described in Patent No. GB-2092388. The relay means comprises a miniature electromagnetic relay which is mounted on a printed circuit board fitted underneath the cover. The contacts of the relay isolate the low tension circuit of the ignition coil. The leads to the two terminals of the relay coil, together with the positive and negative supply leads, are fed through an armoured flexible tube, which connects the coil cover to a key means in the form of a sealed multipin plug mounted inside the passenger compartment of the vehicle, preferably close to the ignition switch, and these four leads are terminated on four of the pins inside the plug sealed housing. A key to operate the immobiliser consists of a detachable socket which mates with the plug and has two pairs of its contacts connected together so as to complete the circuit for the relay.

A large number of combinations for the wiring of the four leads to the pins is available, the number depending on the total number of pins on the plug. A different wiring combination which will be unique can be allocated to each individual immobiliser until all the combinations have been used, when the sequence is repeated. The combination is selected at random and this can be done conveniently by use of a computer program.

When the correct key is inserted and the vehicle ignition switched on, the relay will operate and so complete the electrical circuit to the low tension side of the ignition coil. When the key is withdrawn the relay is de-energised and the low tension circuit of the coil is isolated. The relay, its associated components and all the wiring to and from the plug are contained either inside the coil cover or inside the armoured flexible tube, making access to them impossible except by the use of cutting tools, and only by gaining access to these wires and correctly connecting them together can the vehicle be started without the correct key in place. Since the four leads to the fixed plug only have to carry the relay current, thinner wires can be used and all four wires can easily pass down the armoured flexible tube. A much smaller plug and key with a larger number of pins can be used since they also only carry the relay current. One type of plug and key used in this invention has 12 pins which increases the number of combinations available.

In order to avoid the risk of the key accidentally coming away from the plug, a key with a self latching feature is used. The key cannot then be withdrawn from the plug without first releasing the latching feature. The small plug can be conveniently mounted adjacent to the ignition lock in the vehicle.

The immobiliser key is small and can be coupled to the ignition key by a light chain, thus ensuring that it is withdrawn with the ignition key. The ignition key together with this small key are not bulky items to carry.

A small diameter armoured flexible tube can be used with the thinner wires to the fixed plug. No wires are carried outside the armoured flexible tube. These improvements together with the much smaller fixed plug make it easier and neater to install the immobiliser in a vehicle and increase the security of the device.

The very small size of the fixed plug makes it extremely difficult for anyone using a measuring instrument to determine the correct combination in order to complete the circuit without using the correct key.

As the relay coil is in a direct current circuit, the relay will operate if the current is applied in either direction. A diode is inserted in the relay circuit so that it will only operate if the current is supplied in one direction. This increases the combinations available in the plug and key and reduces the risk of anyone being able to determine the correct combination.

Power to the low tension side of the ignition coil is usually supplied by two electrical leads, one which comes from the vehicle ignition switch circuit and the other which is connected to the contact breaker. In order to facilitate the connections to the ignition coil, a multiway terminal block is mounted on top of the coil cover. The insulation component of this block may be provided by a plastics moulding or another suitable material. Conveniently this can be a four-way terminal block but a block with more ways may also be used in order to increase the complexity of the immobiliser, such as using a double-pole change-over relay and using the second set of contacts to immobilise another circuit such as the starter motor.

To fit the coil cover to the ignition coil, the two low tension leads to it have to be removed from their respective terminals on the coil. Two leads from the printed circuit board are attached to the terminals on the ignition coil before the cover is closed. The two leads from the vehicle's electrical system which were removed from the coil are attached to the correct terminals on the terminal block on top of the coil cover.

The positive electrical supply for the relay is derived from the lead from the vehicle's ignition circuit. The negative supply is provided by an earth lead which is connected to one of the four terminals. By using a change-over relay if the key to operate the relay is not inserted and the vehicle ignition switch turned on, the relay will not be energised and its normally closed contact will become live. This can be used to power a siren or other warning device.

In order to protect the electrical circuit from someone tampering with it, an electrical fuse can be inserted in the positive lead to the coil. With the vehicle ignition switch on but no key inserted, if anyone accidentally or deliberately touches the pin in the fixed plug which is connected to the positive supply and shorts it to earth, the fuse will blow.

An alternative means of protection, which may be used in accordance with this invention, comprises a relay with a coil voltage substantially below the supply voltage: the relay is then operated with a series resistor which is placed in the part of the circuit leading to the plug. If the live pin is accidentally connected to earth, current will flow through the resistor. The value and wattage rating of the resistor are chosen so that the current is not excessive. The resistor will heat up but without any other damage.

In order that the armoured flexible tube may be coupled to the cover over the ignition coil as described in Patent GB2092388, a small detachable connector is fitted to the four wires where they emerge from the armoured flexible tube. The detachable connector, which can pass through the hole in the side of the top coil cover, fits to a mating plug mounted on the printed circuit board. This detachable connector may conveniently be a miniature plug/socket similar to ones commonly used on printed circuit boards. The ignition coil end of the armoured flexible tube has a metallic grommet fitted to it so that it can form a self-locking feature with the coil cover as described in Patent No. GB-2092388.

To prevent the electrical leads being drawn up the armoured flexible tube in the event of the tube being cut, the electrical leads are cemented in the ends of the tube with a suitable adhesive.

One means of making the electrical connections between the terminal block and the printed circuit board comprises double-ended shoulder rivets which also act as mounting posts for the printed circuit board. Insulation between the metal rivets and the metal coil cover is provided by the terminal block and a thin plastics film inside the coil cover.

Alternatively the plastics film may be replaced by a plastics moulding. Access to the connections on the coil is restricted by the coil cover and if the terminal block is forcibly removed from the top cover, only four small holes are presented and it is not possible to make connections to the ignition coil through them.

It is a preferred feature that the immobiliser arms automatically when the ignition is switched off. Preferably however, a delay is built into the relay means, such that the immobiliser arms only after a predetermined delay from switching off the ignition: preferably the immobiliser includes an LED (e.g. green) which is energised continuously when the immobiliser is unarmed, then flashes at high repetition rate during the delay (e.g. 30 seconds) after switching off the ignition, then the same or another (e.g. red) LED flashes at a slower rate when the immobiliser becomes armed. The electrical leads to the LED(s) may also pass through the armoured cable from the relay housing to the key means, and the LED(s) may be mounted on the fixed plug housing of the key means.

In a further embodiment of the invention, the circuit incorporating the control line can be isolated from the electronic latching circuit by means of an opto-isolator, thus improving security by removing the risk of spurious signals triggering the latching circuit. The electronic circuit may be arranged to operate with a supply voltage of either polarity, by incorporating appropriate rectifier arrangements: the immobiliser can then be used, without change, on vehicles having negative earth or positive earth.

Preferably the immobiliser includes a facility for isolating a second circuit, e.g. the fuel pump or the starter, at the same time as isolating the ignition coil. Thus, preferably a pair of terminals for connection into the secondary circuit are included on the housing, which encloses the relay means, on the coil. Preferably all of the electrical and electronic circuitry of the immobiliser is enclosed within the housing on the ignition coil (apart from the leads which pass through the armoured cable to the key means).

Preferably the relay means of the security device or immobiliser is of a self-hold type, such that it latches on once initially energised, and so that only momentary actuation of the key is necessary. I have devised a low cost key which may be used in such circumstances but which may be used for applications other than vehicle immobilisers.

Thus, in accordance with this invention, there is provided a key for making momentary contact with the pins of a mating device, said key comprising a printed circuit board formed with plated through-holes, the circuit board being printed with at least one track which connects a pair of said plated through-holes.

Separate printed circuit boards are used for each wiring combination, with the required links between the contacts being formed by printed tracks between appropriate through-holes. There is no hand-wiring to be done and so the key can be made and assembled at low cost and with no risk of wiring errors.

Embodiments of this invention will now be described, by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a schematic diagram of the electrical circuit of an immobiliser in accordance with this invention; FIGURE 2 is a view of a multipin plug, including its armoured flexible tube, and a key of the immobiliser of Figure 1; FIGURE 3 is a top plan view of a coil cover with a terminal block of the immobiliser in place; FIGURE 4 is an underside view of the coil cover with a printed circuit board of the immobiliser in place; FIGURE 5 is a cross-sectional view of the coil cover of the immobiliser fitted to a typical ignition coil; FIGURE 6 is a detailed cross-section of part of the coil cover and terminal block; FIGURE 7 is an enlarged view of a typical commercial miniature plug assembled with its armoured electrical lead; FIGURE 8 is a view of a low cost key in accordance with this invention and mating with the fixed plug of Figure 7; FIGURE 9 is an enlarged front view of a miniature printed circuit board used in the key of Figure 8; FIGURE 10 is an enlarged rear view of the miniature printed circuit board of Figure 9, with one possible arrangement of printed circuit tracks connecting together two pairs of plated through-holes; and FIGURE 11 is a much enlarged view showing the end of a pin in the fixed plug making contact with the corresponding plated through-hole in the circuit board when the key is mated with the fixed plug.

Referring to Figure 1, the four-way terminal block 1 is the terminal block which is mounted on the top of the coil cover 29 shown in Figures 3 and 4. The two leads 2 and 3, which have been removed from the low tension side of the ignition coil, are connected to the terminal posts 4 and 7 respectively on the terminal block 1. The other ends of the leads 2, 3 come from the vehicle electrical system. Lead 2 is derived from the ignition switch circuit and lead 3 is connected to the contact breaker. These parts of the vehicle's electrical system are shown in simplified form for clarity, in Figure 1.

A relay, which has a relay coil 8 and associated contact 9, is mounted on a printed circuit board together with a diode 10, resistor 11 and a four-way connector 12. Two leads 13 and 14 connect the circuit on the printed circuit board to the low tension terminals on top of the ignition coil.

In Figure 1 the connection loops 15 and 16 represent in diagrammatic form the parts of the circuit formed by the leads to the plug and key and back again, when the correct key is engaged.

In order to complete the circuit, an earth wire 17 is taken from the terminal 6 on the terminal block 1 and is connected to a suitable point on the vehicle chassis.

With the correct key engaged and the ignition switch switched on, a circuit is made from lead 2 via resistor 11, loop 15, diode 10, relay coil 8 and loop 16, to the earth wire 17. When this circuit is energised, the relay contacts 9 will change over making a circuit via lead 19, contacts 9, lead 13, the low tension side of ignition coil 20, lead 14 and lead 3.

The ignition coil will now operate normally.

Figure 1 also shows an alarm such as a siren 21 connected to terminals 5 and 6 on the terminal block 1. If the ignition switch is switched on without the immobiliser key in place, loops 15 and 16 will not be made. A circuit is then made from terminal 4 via lead 19, contacts 9, lead 18, terminal 5, siren 21, terminal 6 and earthwire 17. The siren 21 will sound and will draw attention to the fact that an attempt is being made to start the vehicle without the key in place.

Figure 2 shows the fixed plug with its housing 23, which is clamped on to the armoured flexible tube 24. Metallic grommet 25 is rigidly fixed to the other end of the armoured flexible tube 24. The four-way connector 26, shown diagrammatically, is fitted to the external end of the four wires which pass through the armoured flexible tube 24 and at the other end these wires are terminated to the rear ends of the pins 27 which are located inside the housing 23. The four wires are terminated on four separate pins of the plug in the selected combination, leaving the remaining pins unconnected.

A seven pin plug is shown for clarity, but a plug with at least 12 pins is used in order to give a large number of unique combinations before the sequence has to be repeated.

In order to assemble the immobiliser, connector 26 in Figure 2 is passed through the hole in the cylindrical portion of the top coil cover (which is described as the outer casing member in Patent GB 2092388). The connector 26 shown diagrammatically in Figure 2 can then be fitted to plug 12 which is mounted on the printed circuit board.

The immobiliser key 28 is a detachable socket which mates with the plug 22. Key 28 has two pairs of its connections coupled together. The pairs correspond to the pairs in the plug 22 which have been terminated. The connections inside key 28 are made so that they will complete the circuit. The whole assembly in Figure 2 with the key in place is represented diagrammatically by the loops 15 and 16 in Figure 1.

Figure 3 is a view looking down on the top coil cover 29. The terminal block 1 sits on the upper surface of this cover 29. It has four terminals 4, 5, 6 and 7, which are twin blade type terminals for push-on connectors. The terminals 4, 5, 6 and 7 are held in position by double ended shoulder rivets 35.

The terminal block 1 has vertical fins 30, 31, 32, 33 and 34 which are part of the same moulding. These fins separate the terminals 4, 5, 6 and 7.

Figure 4 shows the underside of the top coil cover 29 with the printed circuit board 36 in position. The printed circuit board 36 is a single-sided board with the circuit tracks on the top side and the components underneath. the printed circuit board is held in position by the other end of the rivets 35. One lay-out for the components on the printed circuit board is shown. Relay 37, which contains relay coil 8 and contacts 9, is mounted on the printed circuit board 36, together with diode 10, resistor 11, four-way plug 12 and two blade terminal posts 40 and 41.

Figure 5 is a part vertical section which shows both the top coil cover 29 and the bottom coil cover 42 fitted in position on a typical ignition coil 43. The bottom cover 42 is held in place on the ignition coil 43 by its turned-in peripheral flange 44 engaging on the lower shoulder rim 45 of the ignition coil and a circlip 46 which engages in a peripheral groove 47 formed internally of the bottom coil cover 42. The circlip 46 bears on a suitable packing washer 48 which sits on the top of the ignition coil rim 45. The top and bottom covers 29, 42 fit together as described in British Patent GB 2092388. The metallic grommet 25, which is on the end of the armoured flexible cable 24, cannot be removed once the top and bottom covers 29, 42 have been assembled correctly.

In Figure 5, the central fin 32 shown in Figure 3 has been omitted from terminal block 1 to show the detail of the double blade terminal 6. The rivets 35 have the dual purpose of supporting the printed circuit board 36 and acting as conductors between the terminals 4, 5, 6 and 7 and the circuit tracks on the printed circuit board.

The four wires which emerge from the armoured flexible tube 24 have their own insulating sheath and form a cable 49.

The connector 26 which is fitted on the end of cable 49 fits and locks to plug 12 on the printed circuit board 37. Two short leads are connected to the terminals 40 and 41 on the printed circuit board 36 and the other ends of these leads are connected to the terminal posts 50 which are on the ignition coil. Only one such post 50 can be seen in Figure 5, the other being hidden by the high tension insulator 51: both of the short leads have been omitted for clarity. These leads must be connected before the two coil covers 29, 42 are closed.

Figure 6 is a detailed cross-section to illustrate one arrangement to connect the terminals 4, 5, 6 and 7 to the circuit tracks 54 on the printed circuit board 36. The terminal block 1, which is made of a suitable insulating material, has three separate annular extensions 51 which pass through holes in the metal top cover 29 underneath terminals 4, 5 and 7. A thin sheet of insulating material 52, which may be a plastics sheet or other suitable material, is fitted underneath the top cover 29 and is held in position by the upper shoulder 53 of metal rivet 35. These two pieces of insulation prevent the rivets 35 from coming into contact with the metal top cover 29. The lower shoulder of rivet 35 sits on top of the circuit track 54 which is on the upper side of the printed circuit board and makes electrical contact with it.

The lower shoulder of the rivet may also be soldered to the circuit track. The lower end of the rivet 35 is rivetted onto a metal washer 54. The insulating material 52 is omitted under the rivet which connects to terminal 6, so that this rivet makes direct contact with the metal top cover 29: the hole in the top cover for this rivet is smaller in diameter as it does not have an annular extension from the terminal block.

Terminal 6 is connected to the earth wire and this ensures that the whole of the cover, the armoured tubing 24 and the plug housing 23 are effectively earthed.

Returning to Figure 1, in a preferred modification the relay 8 is a self-holding type, such that the contacts 9 remain picked-up (completing the circuit via lead 13 to the ignition coil 20) if the key 28 is removed, and until the ignition switch is turned off. Thus the key 28 only needs to be inserted momentarily, whilst the ignition switch is turned on, in order to enable the ignition circuit.

A preferred form of key, for use where such a momentary contact is required, will now be described with reference to Figures 7 to 11 of the drawings. It will be appreciated that this key has uses other than for vehicle immobilisers such as that described above.

Referring to Figure 7, a fixed plug 62 is shown without any means of support. It is normally mounted in a convenient position and in a motor vehicle may be mounted directly into the fascia panel or in a suitable mounting bracket fixed underneath the fascia panel. The fixed plug is a typical commercial product, typically with twelve contact pins 61. The fixed plug 62 has internal slots 63 in order to locate the key (also in the form of a plug) correctly when it is inserted.

At the rear of the fixed plug 62 there is a collet-type clamping arrangement 64 which clamps onto an armoured cable 65 which protects the wires 66 connecting the plug 62 to the remainder of the electrical circuit. After assembly the collet clamp 64 is locked and sealed with a suitable adhesive or locking compound so that it is extremely difficult to attack the wiring.

Referring to Figure 8, the key 67 has external locating formations 68 which correspond to the slots 63 in the fixed plug 62 of Figure 7. The miniature printed circuit board 69 is shown in position at the bottom of the cylindrical bore 70 in the end of the key 67 so that its plane is perpendicular to the axis of the key. The key 67 may be conveniently made as a simple plastics moulding from a suitable material such as glass-filled nylon and the printed circuit board 69 is made so that it is a tight fit in the cylindrical bore 70. It is also held in position by means of a suitable adhesive.

The miniature printed circuit board 69 is shown in Figure 9, which further shows the ends of the plated throughholes 71 with their surrounding pads. The printed circuit board is made by conventional manufacturing techniques with copper tracks and plated through-holes. The plated throughholes 71 are situated in positions which correspond to the positions of the pins 61 in the fixed plug 62. The printed circuit board 69 has a locating key 72 on its outer diameter, which locates in a slot 73 in the cylindrical bore 70 in order to provide correct location in the key 67 so that its plated through-holes will align with the pins 61 when it is mated with the fixed plug 62. The rear side of the printed circuit board 69, as shown in Figure 10, carries the printed circuit tracks 74 which link two pairs of plated through-holes together. When the miniature printed circuit board is assembled in the key-67, the tracks are hidden so that the combination of the connection used cannot be seen. Each miniature circuit board will have different tracks according to the arrangement selected. There are 1485 unique layouts for the tracks thus giving 1485 differs. After all the differs have been used, the sequence is repeated. Each key 67 may be numbered for reference. The particular track combination used for each key and its mating fixed plug may be selected on a random basis using a computer.

The copper tracks and plated through-holes of the printed circuit board 69 may be overplated with nickel and gold or other metals to give improved properties such as wear and corrosion resistance. The printed circuit board may also be screen printed with a coating such as a solder resist or treated with another type of protective coating. The depth of the cylindrical bore 70 is such that when the printed circuit board is in position and key 67 is inserted into the fixed plug 62, the ends of the pins 61 just enter the plated throughholes.

A typical pin 61 is shown in a much enlarged view in Figure 11. Only part of the conical end 75 of the pin 61 enters the plated through hole 71 when the key 67 is mated with the fixed plug 62 and electrical contact is made between part of the surface of the conical end and corner 76 of the plated through-hole.

The locating formations 68 on the key 67 are made with relatively loose fit with the slots 63. This ensures that even if there is a small variation in the length of the pins 61 through normal manufacturing tolerances, by a slight rotation of the key 67, contact will be made between the pins 61 and the plated through holes 71. This rotation tends to be a natural hand movement. Only momentary contact is required, since once correct contact has been made the electrical circuit latches into a new state and the key 67 can be withdrawn.

In one type of immobiliser circuit an indicator light, which can be conveniently provided by a light emitting diode, changes form a flashing state to a continuous state when correct contact has been made, thus indicating that the key 67 may be withdrawn. It is desirable that similar security circuits should also have some form of indicator to show the change of status when contact has been made after the key 67 has been inserted.

The key 67 has a hole 76 in its end for the insertion of a split ring so that the key-plug may be conveniently linked to a key ring such as that on a typical vehicle ignition key.

Claims

1) A key for making momentary contact with the pins of a mating device, said key comprising a printed circuit board formed with plated through-holes, the circuit board being printed with at least one track which connects a pair of said plated through-holes.

2) A key as claimed in claim 1, in which said printed circuit board includes a plurality of redundant said plated through-holes, for mating with corresponding, redundant said pins of the mating device.

3) A key as claimed in claim 1 or 2, comprising a housing in which said printed circuit board is mounted, said housing being arranged for coupling in a predetermined orientation with said mating device so that the ends of said pins partially enter said plated through-holes of the printed circuit board.

4) A key as claimed in claim 3, in which said key housing comprises a portion of cylindrical shape for coupling with a complementary-shaped portion of said mating device.

5) A key as claimed in claim 4, in which said cylindrical portion of said key housing is provided with formations for engaging with complementary formations on said mating device, to determine the relative angular orientations in which said key housing and mating device couple together.

6) A key as claimed in claim 5, in which said formations on said key housing and on said mating device permit limited relative rotation between said key housing and said mating device.

7) A vehicle security device which comprises a relay means operable to complete a circuit to the primary of an ignition coil, and a control line for the relay means extending to a remote key means which serves to actuate the relay means and complete said circuit, the relay means being enclosed within a secure metal cover which fixes over the top of the ignition coil.

8) A vehicle security device as claimed in claim 7, in which said control line extends through an armoured cable or duct from said relay means to said key means.

9) A vehicle security device as claimed in claim 7 or 8, in which said control line comprises two or more electrical wires through which a circuit is completed, when the remote key means is actuated, to operate the relay means.

10) A vehicle security device as claimed in claim 9, in which the remote key means comprises a main part secured to said control line and a key for coupling to said main part, for interconnecting at least one predetermined pair of a plurality of said electrical wires.

11) A vehicle security device as claimed in claim 10, comprising a self-latching feature for retaining said key engaged with said main part of the remote key means.

12) A vehicle security system as claimed in claim 10, in which said relay means is of a self-hold type, arranged to latch on in response to momentary engagement of said key with said main part of the remote key means.

13) A vehicle security device as claimed in any one of claims 7 to 12, arranged so that said relay means is deactuated only after a predetermined delay from switching off the vehicle ignition switch.

14) A vehicle security device as claimed in any one of claims 7 to 13, in which said control line is isolated from the relay means circuit by an opto-isolator.

15) A vehicle security device as claimed in any one of claims 7 to 14, in which said relay means also serves, when actuated, to enable an additional circuit or circuits, for example the fuel pump or starter circuit.

16) A key as claimed in claim 1 and substantially as herein described with reference to Figures 7 to 11 of the accompanying drawings.

17) A vehicle security device as claimed in claim 7 and substantially as herein described with reference to Figures 1 to 6 of the accompanying drawings.

18) A vehicle security device as claimed in any one of claims 7 to 15 and 17, which includes a key as claimed in any one of claims 1 to 6 and 16.