Introduction:
The car alarm provides security for the car. The different classes indicate which security features are connected to the system. The higher the class, the more extensive it is. Some insurers also give discounts on premiums (often only when an official certificate has been issued).
Different classes:
- Class 1: immobiliser
- Class 2: class 1 + alarm system with siren, ultrasonic sensors or a radar
- Class 3: class 1 + 2 + siren including backup battery, tilt detector
- Class 4: class 1 + 2 + 3 + vehicle tracking system
- Class 5: all systems from class 1 to 4.
The difference between class 4 and 5 is that the vehicle tracking system is activated when the alarm goes off. With a class 4 system this is not the case.
All systems mentioned here are described in the following chapters.
Immobiliser:
A class 1 security system has an immobiliser (sometimes also called a starter interlock). The key contains a transponder that holds a code. The control unit of the car’s immobiliser must recognise (and approve) this code before the engine can be started.
Alarm control unit:
The control unit receives signals from the door locks, ultrasonic, tilt and/or radar sensor. If a signal comes in while the alarm is activated, the control unit switches on the siren and the indicators. The device is activated as soon as the car is locked with the remote control. Locking the car mechanically with the key will not activate the system.
- Cars without CAN bus: the existing central locking control unit sends the signals from the doors, boot and bonnet to the separate alarm control unit. When retrofitting, wires will need to be run to connect to the existing wiring. This includes, among other things, the wiring of the indicator circuit.
- Cars with CAN bus: the alarm control unit will be connected to the 2 CAN bus wires of the comfort circuit. After registering it via a diagnostic computer (thus making it known to the system), no separate wires will need to be run as in a car without CAN bus. The signals travel across the complete CAN bus network and also reach the alarm control unit.
Siren:
When the alarm system (class 2, 4 or 5) is activated and the sensors in the car detect that someone is inside the car (ultrasonic or radar), a door is opened (signal from the door locks), or when the car is jacked up (tilt detection), the alarm control unit activates the siren. Most sirens produce a sound level of around 125 dB. Each manufacturer uses its own tone. Some make a beeping sound, others make a sound with as many different pitches as possible. The siren can be installed in many different places. The most commonly used locations are: the wheel arches, the engine compartment or under the cowl panel.
A siren of an alarm system with class 3 has a backup battery. If the alarm goes off and the battery terminal is disconnected, the backup battery will continue to supply power to the siren. The siren will continue to sound for several more minutes. It is strongly recommended to replace this backup battery every few years (consult the manufacturer’s data for this). Nowadays a fault is often stored in memory when the battery is about to run flat.
Ultrasonic sensors:
The ultrasonic sensors monitor the interior for movement. Ultrasonic sensors work, as the name suggests, with ultrasonic waves (just like the Park Distance Control sensors). The sensors transmit and receive the ultrasonic waves. The time between transmission and reception is measured. When the alarm is activated, these sensors calibrate the system during the first minute after switching on. The distance between the sensors and the objects in the interior (e.g. the seats) is stored in the system. As soon as movement occurs in the car (for example when a window is smashed), the ultrasonic waves collide with this object or person and this affects the time between transmitting and receiving. The control unit of the alarm system will immediately activate the siren.
The ultrasonic sensors not only register movements of objects, they are also sensitive to vibrations. When the car is parked with the windows closed, the air in the interior will not move either. As soon as the windows are opened, air flows through the car and the sensors will register this. The alarm will then go off. If the sensitivity is set very high, the alarm can also be triggered by loud noise outside the car. This noise can be caused by fireworks or thunder. That is because sound is purely a vibration in the air. As soon as the sound is loud enough and this vibration can enter the interior of the car, the ultrasonic sensors will register it. Because the sensors are sensitive to sound vibrations, they are not suitable for convertibles. If the roof is open and the alarm were activated, it would go off constantly. That is why convertibles do not have ultrasonic sensors, but instead have a radar.
Radar:
Not only for driving assistance, but also for the alarm system a (different type of) radar can be used. The radar of the alarm system is concealed as centrally as possible in the interior (see image below). The radar emits radar signals that are not dependent on sound waves, vibrations and movements of fast, small objects. That is why radar is suitable for a convertible, whereas a system with ultrasonic sensors is not. Compared to the ultrasonic sensor, the radar is very slow and will only trigger the alarm several seconds after a person has sat down in the car. This system also needs to calibrate itself after the alarm is activated. The radar will also not be limited to only the interior of the car. The radar signals pass straight through the metal and plastic of the car (and are weakened as a result) but will still register movements that occur directly next to the car. This makes it possible to adjust the radar so that when someone walks too close to the car (or touches it) the alarm is activated.
Tilt detection:
In the middle of the interior, often in the centre console, the tilt detector is installed in a class 3 alarm system. This sensor measures the position in which the car is located, because a small ball takes a certain position. When the alarm is activated, the position of the movable ball is measured. As soon as the system has calibrated itself after about a minute, the position is monitored.
As soon as the car adopts a different position, for example because it is being jacked up, the ball moves further in the sensor. This movement is recognised and the alarm is activated. The car may, for example, be jacked up to remove the wheels, or to tow it away. It does not matter that the car is hanging backwards because there is a lot of luggage in the boot, or that there is a caravan attached. When the alarm is activated, the system is calibrated to the position it is in at that moment. If the caravan is disconnected in the meantime (and the rear rises), the alarm will also go off.
Vehicle tracking system:
With an alarm class 4 or 5, a vehicle tracking system is installed. This is a separate device that is hidden as deep as possible in the interior. It must take as long as possible before a malicious person finds this device. As soon as the alarm is activated, this device will send the GPS coordinates every few seconds via a GSM signal to the control room. The control room (of the alarm system) will immediately alert the police, who will then respond. The tracking system will continue to transmit the GPS coordinates until the alarm system is switched off. This tracking system also contains a backup battery that lasts about 24 hours after disconnecting the car’s battery.
