30.9.
Vehicle Security Systems
Car and alarm manufacturers are constantly trying to improve security against theft. Great achievements have been made recently by incorporating the alarm system as an integral part of the vehicle electronics. Even the retro-fit systems are still very effective. Three main types of intruder alarm are used:
(a) Switch operated on all entry points.
(b) Battery voltage sensed.
(c) Volumetric sensed.
In addition the methods used to disable the vehicle are : (i) Ignition and/or starter circuit cut off.
(it) Engine ECU code lock.
Alarms can be set by a separate switch or IR transmitter. More commonly now, they are set automatically when the doors are locked. Professional car thieves always find ways to maneuver the latest alarm systems. The vehicle manufacturers strive to stay one step ahead. Legislation is being considered for installing tracking devices in an unknown part of a vehicle’s chassis. This can be activated during the theft of the car, allowing the police to trace the vehicle.
30.9.1.
An Overview of Available Systems.
The good alarm systems now available are either retro-fit systems or factory fitted. Most are made for 12 V negative earth vehicles. They use electronic sirens and generate an audible signal when arming and disarming. All of them are triggered when the car door opens and automatically reset after a period of time, often 1 or 2 minutes. The alarms are triggered instantly when the entry point is breached. Most systems are two pieces, with separate control unit and siren. The control unit is installed in the passenger compartment and the siren under the bonnet in most systems.
Most recent systems use two infra-red remote keys, which incorporate small button type batteries and have an LED to indicate when the signal is being sent. They operate with one vehicle only. Intrusion sensors, which detect car movement or use volumetric sensing, can be adjusted for sensitivity.
When operating with flashing lights most systems draw current about 5 A and without flashing lights (siren only) the current drawn is less than 1 A. The sirens produce a sound level of about 95 dB, when measured 2 m in front of the vehicle. A block diagram of a complex alarm
Fig. 30.59. Block diagram of a complex alarm system.
system is shown is Fig. 30.59. The system, as usual, contains a series of inputs and outputs as follows.
Inputs:
• Ignition supply.
• Engine cranks signal.
• Volumetric sensor.
• Bonnet switch.
• Tremble switch.
• IR/RF remote signal.
• Door switches.
• Control switch. Outputs:
• Volumetric transmitter.
• System LED.
• Horn or siren.
• Hazard lights.
• Ignition immobilizer.
• Loop circuit.
• Electric windows, sun roof and door locks.
Some factory fitted alarms are coupled with the central door locking system, known as lazy lock. One press of the remote unit sets the alarm, close windows and sun roof and finally locks the doors.
30.9.2.
Security Coded Electronic Control Units
One of the recent ideas is to use a security code in engine electronic control unit so that it can be unlocked to allow the engine to start only when it receives a coded signal. Ford is using a special ignition key, programmed with the required information. Citroen uses a similar idea in some of their models, but the code has to be entered via a numerical keypad.
Of course with this arrangement also the car can be lifted onto a lorry and driven away, but when this is done a new engine control ECU is required, which is costly.
