Car Alarms - What to Look For When Purchasing a System
The first documented case of car theft was in 1896, only ten years after gas powered cars were first introduced. Since those early days cars have increasingly become a natural target for thieves. They are valuable, relatively easy to steal, fairly easy to resell and have a built in getaway system. Over 500,000 vehicles are taken in the UK every year – one every 55 seconds and a break in and theft from a vehicle happens every 23 seconds. In the USA a car gets broken into every 20 seconds. A stolen car is also 200 times more likely to be involved in an accident, and one in three are never recovered. It therefore makes sense to reduce this risk - one way to decrease the chance of your vehicle being stolen is to fit a quality car alarm and or an immobiliser. The high crime rates have encouraged millions of people around the world to invest in car alarm systems for their vehicles over the last few years.
The car alarms computer control unit monitors signals from all of the sensors and activates the alarm signalling devices – sirens, horns, headlights, emergency lights, mobile phone depending on the system installed. Control units are normally connected to the cars main battery, but will often have a back-up power source as well. This back-up (hidden) battery will kick in if someone cuts the main supply wires to the car alarm and will immediately trigger an alarm condition – sirens etc.
Door sensors – typically fitted to doors, boots/trunks and bonnets/hoods. Most car alarm systems utilise the switches that are already built into most modern cars for switching on internal lights when any of these are opened. Many modern car alarm systems also monitor the voltage in the car's electrical circuit. Whenever there is a drop in this voltage, the control unit knows that someone has interfered with the electrical system – opened a door, bonnet, trunk causing a light to come on, or messed with the wiring. Although door sensors are highly effective, they don't respond if someone climbs through a smashed window, or if they tow your car away, other additional forms of protection are required. Shock sensors – this type of sensor is activated by somebody hitting your car, or moving it in some way. The sensitivity of the units can be adjusted, so that the control unit only activates the car alarm circuits for particular intensity or severity of motion. This overcomes the problem of false alarms caused by the car being rocked by passing vehicles or strong winds. Window sensors – many criminals don't bother with overcoming door locks, they just smash a window to get into your vehicle. This type of intrusion can be detected by some form of glass break detector, the simplest form of which is based on a simple microphone. The microphone measures fluctuations in air pressure and converts them into matching variable frequency electrical currents. As breaking glass has its own distinctive sound frequency (pattern of air pressure fluctuations), the signals are passed through a crossover unit which filters out all other frequencies. This ensures that the control unit only activates the car alarm when glass is broken. Pressure sensors – these monitor air pressure levels inside a vehicle. Even if the air pressure is the same inside and outside the vehicle – the act of opening a door or smashing a window pulls or pushes the air in the car, creating a brief change in pressure. These sensors are in effect loudspeakers in reverse – the movement of the air causes the speaker cone to move back and forth. This in turn pulls and pushes the attached electromagnet, which generates an electric current. When the control unit registers a current flowing from this device it knows that either the air pressure has changed rapidly, or that there has been a loud noise and will therefore activate the alarms. Motion and tilt sensors – many thieves are not after your whole car or what is in it, they want individual parts of your car, such as the expensive alloy wheels, or they may want to dismantle the whole car and sell its parts. They may therefore jack the car up where it is or tow it away for dismantling. To defeat this type of crime vehicles can be fitted with tilt detectors, normally in the form of a mercury switch. Mercury is a liquid metal which conducts electricity and flows like water, making it ideal as a movable contact responding to angle of tilt. Car alarms typically use an array of mercury switches positioned at varying angles, some of which are in the closed position when you're parked on a slope and some of them are in the open position. The control unit responds to the changing state of these switches (some open and some close), caused by jacking or lifting up to tow away.
Different combinations of detectors are used in the various car alarms available on the market and dependant on its sophistication. The most effective car alarms are those linked to an immobiliser, which will normally deactivate fuel pumps, ignition systems and or starter motors. Some car alarm systems will also play a recorded message when someone gets to close or interferes with your vehicle – this may well deter the opportunist type of criminal. Most car alarms now have key-ring transmitters for arming and disarming the alarm systems, often combined with the central locking system. These transmitters have made car alarms much easier to use and overcome the problems associated with the time delay used on the older systems. As well as allowing you time to get out of your car once you had activated the alarm, the time delay also allowed you time to get into the car to deactivate it – this also allowed any criminal the same amount of time to disable the alarm before it sounded. As these transmitters operate on a pattern of pulse modulation, millions of different pulse codes can be used, making individual systems unique, meaning other people can't gain access to your car without having a matching transmitter using the same pulse codes. Even these systems are not foolproof because some criminals have devices called code-grabbers – these are basically radio receivers, which are sensitive to the transmitters signal and are able to receive the code and record it. If the thief can intercept your transmitted disarm code, he/she can then program another transmitter to exactly mimic your unique pulse coded signal. The thief can then completely bypass the alarm system next time you leave your car unattended. To overcome this problem the more sophisticated car alarms generate a new series of codes every time you arm the alarm. The receiver then encrypts this new code and sends it to your new transmitter, allowing you to disarm the alarm when you return to your car. It doesn't matter if this new code is intercepted as it is only used once and is
therefore worthless to any thief.
Changing Views on Car Alarms Most insurers in the UK still recommend that car alarms should be fitted and ideally should be Category 1 or 2 Thatcham approved. In the US, the situation is changing, due to the effect that the ever increasing noise generated by car alarms is adversely having on the general public and their quality of life. Manufacturers, installers, insurers, criminologists, police and thieves all say that car alarms are ineffective at stopping car theft. A 1997 analysis of insurance claims data from 73 million vehicles concluded that cars with alarms show no overall reduction in theft losses compared to cars without alarms. In fact some major manufacturers have begun to phase out factory installation of alarms. Unfortunately people don't respond to car alarms because the majority are false, 95-99% of the time, according to estimates. Alarms do not deter the pros – it is estimated in USA that 80% of cars are stolen by organised crime, around $ 8.2 billion per year. The pros can and do steal cars with alarms
Additional information on car security and hundreds more tips on how to protect your family, is now available in our
new security and safety book
'How to Protect your Family and Belongings Now'
|
