Vehicle Anti-Hijack Alarm

This circuit was designed primarily for the situation where a hijacker forces the driver from the vehicle. If a door is opened while the ignition is switched on - the circuit will trip. After a few minutes delay - when the thief is at a safe distance - the Siren will sound.
Where it differs from the first two alarms - is in what happens next. I'm obliged to Victor Montanez from the USA who suggested that the engine cut-out should not operate - until the vehicle comes to a stop. That way - the engine will not fail suddenly or unexpectedly. And the hijacker will retain control.
I haven't been able to implement Victor's excellent suggestion completely - because I couldn't think of a simple, reliable and universally applicable way of sensing when the vehicle has come to a stop.

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Vehicle Anti-Hijack Alarm 1
Vehicle Anti-Hijack Alarm 2

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Instead - I have postponed engine failure until the ignition is switched off. Once the thief turns off the ignition - the engine will not re-start. Clearly - there is no certainty as to when this will occur. But I think it will occur sooner rather than later. Because there's a strong possibility that the hijacker will turn off the ignition - in an attempt to silence the siren.
As well as acting as a Hijack Alarm - this circuit offers some added protection. Like the Enhanced Hijack Alarm - it incorporates Jeff Chia's suggestion. That is - every time the ignition is switched on - the alarm will trip. So it will protect the vehicle whenever you leave it unattended with the ignition switched off - even overnight in your driveway.

IMPORTANT!!!

Before fitting this or any other engine cut-out to your vehicle - carefully consider both the safety implications of its possible failure - and the legal consequences of installing a device that could cause an accident. If you decide to proceed - you will need to use the highest standards of materials and workmanship.

Notes

You're going to trip this alarm unintentionally. When you do - the LED will light and the Buzzer will give a short beep. The length of the beep is determined by C4. Its purpose is to alert you to the need to push the reset button. When you push the button - the LED will switch-off. Its purpose is to reassure you that the alarm has in fact reset.
If the reset button is not pressed then - about 3 minutes later - both the Siren and the Buzzer will sound continuously. The length of the delay is set by R8 & C5. For extra effect - fit a second siren inside the vehicle. With enough noise going on - you may feel that it's unnecessary to fit the engine cut-out. In which case - you can leave out C7, D8, R12, R13, Ty1 & Ry2.
When the ignition is switched on - C3 & R4 are responsible for tripping the alarm. By taking pin 1 low momentarily - they simulate the opening of a door. If you don't want the alarm to trip every time you turn on the ignition - simply leave out C3 & R4.
Because the voltage on C3 may be reversed - the capacitor needs to be non-polarized. But connecting two regular 22uF capacitors back to back as shown - will work just as well. Because non-polarized capacitors are not widely available - the prototype was built using two polarized capacitors.
To reset the circuit you must - EITHER turn off the ignition - OR close all of the doors - before you press the reset button. While BOTH the ignition is on - AND a door remains open - the circuit will NOT reset.
The reset button carries virtually no current - so any small normally-open switch will do. Eric Vandel from Canada suggests using a reed-switch hidden behind (say) the dash - and operated by a magnet. I think this is an excellent idea. As Eric said in his email: - "... that should keep any thief guessing for a while."

How you prevent the engine from starting is up to you. It should happen when Ry2 de-energizes. The contacts of Ry2 are too small to do the job themselves. So use them to switch the coil of a larger relay. Remember that the relay must be suitable for the current it's required to carry. Choose one specifically designed for automobiles - it will be protected against the elements - and will give the best long-term reliability. You don't want it to let you down on a cold wet night - or worse still - in fast moving traffic!!! Remember also that you must fit a 1N4001 diode across YOUR relay's coil - to prevent damage to the Cmos IC
YOUR relay should drop-out when Ry2 de-energizes. Wire YOUR relay so that when it drops-out the engine will not start. Because turning-off the ignition will cause both Ry2 and YOUR relay to de-energize - the standby current will be low - and the engine will be disabled while the vehicle is parked.
The circuit board must be protected from the elements. Dampness or condensation will cause malfunction. Fit a 1-amp in-line fuse AS CLOSE AS POSSIBLE to your power source. This is VERY IMPORTANT. The fuse is there to protect the wiring - not the components on the circuit board. Please note that I am UNABLE to help any further with either the choice of a suitable relay - or with advice on installation.
Both the Siren and the Buzzer will go on sounding until the alarm is reset. The circuit is designed to use an electronic Siren drawing up to about 500mA. It's not usually a good idea to use the vehicle's own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that Ry1 is too small to carry the necessary current. Connect the coil of a suitably rated relay to the "Siren" output. This can then be used to sound the Horn.

Transistor Based Motorcycle Alarm

This is a simple - easy to build - transistor based motorcycle alarm. It's designed to work at 12-volts. But - if you change the relay for one with a 6-volt coil - it'll protect your "Classic Bike". The standby current is virtually zero - so it won't drain your battery.

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Transistor Based Motorcycle Alarm
Transistor Based Motorcycle Alarm

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Notes

Any number of normally-open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. While at least one switch remains closed - the siren will sound.
About one minute after all of the switches have been opened again - the alarm will reset. How long it takes to switch off depends on the characteristics of the actual parts you've used. You can adjust the time to suit your requirements by changing the value of C1 and/or R3.
The circuit is designed to use an electronic Siren drawing 300 to 400mA. It's not usually a good idea to use the bike's own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that the alarm relay is too small to carry the necessary current. Connect the coil of a suitably rated relay to the Siren output - and use its contacts to sound the horn.
The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Without its terminal blocks, the board is small. Ideally, you should try to find a siren with enough spare space inside to accommodate it. Fit a 1-amp in-line fuse as close as possible to the power source. This is Very Important. The fuse is there to protect the wiring - not the circuit board. Instead of using a key-switch you can use a hidden switch; or you could use the normally-closed contacts of a small relay. Wire the relay coil so that it's energized while the ignition is on. Then every time you turn the ignition off - the alarm will set itself.
When it's not sounding, the circuit uses virtually no current. This should make it useful in other circumstances. For example, powered by dry batteries and with the relay and siren voltages to suit, it could be fitted inside a computer or anything else that's in danger of being picked up and carried away. The low standby current and automatic reset means that for this sort of application an external on/off switch may not be necessary.
When you set the alarm - if one of the switches is closed - the siren will sound. This could cause annoyance late at night. A small modification will allow you to Monitor The State Of The Switches using LEDs. When the LEDs are all off - the switches are all open - and it's safe to turn the alarm on.

Two Simple Relay Based Motorcycle Alarms

These are two - easy to build - relay-based alarms. You can use them to protect your motorcycle - but they have many more applications. If you use relays with 6-volt coils - they'll protect your "Classic Bike". Both alarms are very small. The completed boards occupy about half a cubic-inch - 8 cc. The standby current is zero - so they won't drain your battery.

Circuit Number Five uses a SPCO/SPDT relay - but you really only need to use a SPST relay. If you are going to use the veroboard layout provided - you'll need to use the style of relay specified. But you can build the alarm using whatever style of relay you have available.

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Two Simple Relay Based Motorcycle Alarms A 1
Two Simple Relay Based Motorcycle Alarms A 2

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Any number of normally-open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. When one of the trigger-switches is closed - the relay will energize and the siren will sound.
You can choose what happens next. If you build the circuit as shown, the siren will continue to sound until you turn it off - or until the battery is exhausted. But, if you leave out D3 - the siren will stop sounding immediately the trigger-switch is re-opened.
While you're within earshot of your machine - the former configuration is best. You can always turn off the alarm yourself. But if you are going to be away from your bike for any length of time - and you don't want to cause a nuisance - then the latter configuration is probably more suitable. If you include a SPST switch in series with D3 - you can select the behaviour that best suits the circumstances at any given time.

Relay coils and some sounders produce high reverse-voltage spikes that will destroy sensitive electronic components. D1 and D2 are there to short-circuit these spikes before they can do any damage. Although there is nothing in the alarm circuit itself that could be damaged - I have no idea what other electronic equipment might be connected to the same power supply. So I included the two diodes as a precaution. If you're satisfied that there's nothing on your bike that might be damaged in this way - you can leave out the two diodes.

Circuit Number Six uses a DPCO/DPDT relay - but you really only need to use a DPST relay. If you are going to use the veroboard layout provided - you'll need to use the style of relay specified. But you can build the alarm using whatever style of relay you have available.


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Two Simple Relay Based Motorcycle Alarms B 1
Two Simple Relay Based Motorcycle Alarms B 2

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Any number of normally-open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. When one of the trigger-switches is closed - the relay will energize and the siren will sound.
You can choose what happens next. If you build the circuit as shown, the siren will continue to sound until you turn it off - or until the battery is exhausted. But, if you leave out the (yellow) solder-bridge in the top left-hand corner of the diagram - the siren will stop sounding immediately the trigger-switch is re-opened.
While you're within earshot of your machine - the former configuration is best. You can always turn off the alarm yourself. But if you are going to be away from your bike for any length of time - and you don't want to cause a nuisance - then the latter configuration is probably more suitable. Connect a SPST switch in place of the (yellow) solder-bridge - and you can select the behaviour that best suits the circumstances at any given time.

Relay coils and some sounders produce high reverse-voltage spikes that will destroy sensitive electronic components. D1 and D2 are there to short-circuit these spikes before they can do any damage. Although there is nothing in the alarm circuit itself that could be damaged - I have no idea what other electronic equipment might be connected to the same power supply. So I included the two diodes as a precaution. If you're satisfied that there's nothing on your bike that might be damaged in this way - you can leave out the two diodes.

General Points

Whichever alarm you build - the circuit board and switches must be protected from the elements. Dampness or condensation will cause damage. Without the terminal blocks - the board is small. Ideally, you should try to find a siren with enough spare space inside to accommodate it. Fit a 1-amp in-line fuse as close as possible to the power source. This is Very Important. The fuse is there to protect the wiring - not the circuit board. Instead of using a key-switch you can use a hidden switch; or you could use the normally-closed contacts of a small relay. Wire the relay coil so that it's energized while the ignition is on. Then every time you turn the ignition off - the alarm will set itself.
When the alarms are not sounding - the circuits use no current. This should make them useful in other circumstances - where a power supply is not readily available. Powered by dry batteries - with the relay and siren voltages chosen to suit - the alarms could be fitted almost anywhere.