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How a car's alarm system works

How a car's alarm system works

The sound of car alarms going off at the touch are common enough. How do these car protection systems detect intrusion?

In a car alarm system, a siren is connected to a few sensors to ensure that as soon as a person opens a door, a signal is transmitted to the wailer from the sensor. Current car alarms are more sophisticated in terms of how they function and the safety features they come with.

There are components or devices like radio receivers, motion detectors, pressure sensors, auxiliary batteries, etc, that enable the alarm to function efficiently, even if the main battery of the car fails.

The Brain
The main part of the alarm system called the brain, a computer control unit, is designed and used to monitor everything that happens regarding the alarm. It triggers the alarm when required. It is connected to all the sensors that are installed in a car.

Car-alarm Transmitters
Most car alarm systems come with some sort of portable keychain transmitter. With this device, we can send instructions to the brain to control the alarm system remotely. This works in basically the same way as radio-controlled toys.

Shock Sensor
Sophisticated modern-day sensor alarm systems make use of shock sensors to ensure that thieves return empty handed. Shock sensor alarms run on the concept of motion strength. Signals to the brain of the system by the sensors determine the strength of the motion and can detect whether someone is trying to push or move the car. The brain of the system immediately gets the horn honking or activates the audio system to start playing loudly in order to ward off the unwanted person/thief.

Motion and Tilt Sensor

  • More than 50,000 cars are stolen every year in the country and less than 15,000 are traced.
  • In India, a vehicle is stolen every six minutes.
  • The loss estimated due to stolen cars is Rs 1,000 crore* per year. Most of the stolen vehicles are passenger cars.

Source: Delhi Police and Transport Department. *2005 figures
This is another type of sensor alarm system which is used to nab thieves who tow away the car between places. Perimeter Scanners are installed in these sensor systems, which are used in order to watch the car's surroundings, like it were a Smart-Eye.

Pressure Sensor
This type of sensor system checks and monitors the changes experienced in air pressure created when a window is broken or cars doors are forcibly opened. When a suspicious pressure change is detected, the alarm is triggered. Some pressure sensors employ the in-built speakers of the car, while many others have their own speakers.

Window Sensor
Without the doors of a car being meddled with, a car can still be stolen by just breaking the windows. This is a trick used by thieves many a time. To prevent such a theft, window sensor alarms are used. The basic window sensor alarm can detect glass or window breakage, using a microphone to pick up the sound of breaking glass.

Door Sensor
The door sensor alarm is probably the simplest of all car alarms. When the front trunk or doors of the car open, the system gets activated and the alarms start ringing. Many door sensor alarms don't need a dedicated switching mechanism to function. They usually require just one addition/element to the wired circuit in order to have the alarm activated.

The Alarm Sounds
Unless the car alarm system gets prompted and a signal to prevent the theft is transmitted, a car alarm does no good for what it is created, regardless of how hi-tech and stateof-art the system it is. The least a car alarm system can be expected to do is to turn on the lights and turn them off (blink/flash), accompanied by noise, in case of intrusion.

Today's thieves are smart and the auto alarm won't stop them, but it might alert someone. The witness who looks out the window, sees someone jump into a car and another car speed away before the first car's alarm cuts off, realises that something is seriously wrong. He or she might even go as far as to call a policeman who might be patrolling the grounds. If your neighbours knows it is your car, and they see someone else jumping in and speeding away, a knock on your door lessens the time before the police are notified, increasing the chances of recovery.

- Text by Santosh Kushwaha

Courtesy: Gadgets and Gizmos