MOST of us have car alarms already installed in our cars, probably one fitted from the factory. While those are satisfactory, it is by no means foolproof as cars are consistently being stolen. Your car alarm might be the same as many of your neighbours, thus the sound of a car alarm in the night may not even be the deterrent it should be. It is not my car alarm until you walk up to an empty parking spot where your car was parked last night.
Basically, your car alarm is an array of sensors attached to a siren. Most car alarm systems utilise the switching mechanism that is built into the doors. In modern cars, opening a door or boot switches on the interior lights. When the door is closed, it presses in a small, spring-activated button or lever, which opens the circuit and vice-versa. If you have this alarm system in your car, you should look into getting something better.
A more sophisticated alarm system would include switches, pressure sensors and motion detectors and a siren that can create a variety of sounds so that you can pick a distinct sound for your car. It would also have an auxiliary battery so that the alarm can operate even if the main battery gets disconnected. A computer control unit, which is a small device, monitors the vehicle. Security systems differ mainly in which sensors are used and how the various devices are wired into the main computer.
The most basic element of a car alarm system is the door alarm. When you open the front hood, trunk or any door of a fully protected car, the computer triggers the alarm system unless you have disarmed it using a control unit or car key.
The cheapest car alarms rely only on door sensors. Advanced alarm systems mostly depend on shock sensors to deter thieves and vandals. A shock sensor is fairly simple: If somebody hits, bumps or otherwise moves your car, the sensor sends a signal to the main computer, indicating the intensity of the motion. Depending on the severity of the shock, the car will sound a warning horn beep or the full-scale alarm.
Sometimes, a thief will break your car window to get at something or to enter the vehicle. A fully equipped car alarm system has a device that senses this. The sensor measures either air pressure fluctuation or a sound frequency to sound the alarm. This is why sometimes a car alarm goes off in hot weather by itself. Or a particularly loud Ducati passes beside the car. By the way, it is not the sound that does it, it is the sound waves that trigger the alarm. Some of the sensors are connected to your car’s speakers because they are sensitive electromagnetic cones.
Some thieves steal a car to strip it down into saleable pieces. They don’t open a door or break a window as a tow truck is their weapon of choice. But a sophisticated alarm will utilise different sensors for this. Some alarm systems include perimeter scanners, which is a radar system, consisting of a radio transmitter and receiver. The transmitter sends out radio signals and the receiver monitors the signal reflections that come back. It measures the proximity of any surrounding object and utilises a delay to prevent unintentional triggering. A warning beep or even a message can be played back if the object of person is loitering close to your car. Some systems include a tilt sensor, which detects if the car has been moved from its parked position. This will trigger the alarm.
A basic car alarm system will honk the horn and flash the headlights when a sensor indicates an intruder. More sophisticated ones may be wired to shut off the ignition starter, cut off the gas supply to the engine or disable the car by other means. A good alarm system will send a message directly to your car key or even handphone.
The primary purpose of the car key or transmitter is to give you a way to turn your alarm system on and off. Usually, the car will flash its lights and honk when you arm or disarm your car. This indicates the alarm system is working. Some will even arm themselves without any input after a preset time. However, an equally sophisticated thief will utilise a “code-grabber” to steal the code that is on your transmitter. To address the problem of “code-grabbing”, some new alarm systems use rolling code algorithms, which changes or encrypts a new code every time you press the transmitter.
So, if you value your car, get someone to assess your alarm system and find out if the level of protection is sufficient for your needs. Going through the rigmarole of police reports and insurance claims is sometimes worth the entry price of a good alarm system. Unless you own a particularly “cold” car, I will see you at my accessory shop soon.