 Such systems protect the cars or similar vehicles from theft.
There are different kinds of locking system available in the market using various
principles.
The most common locking system gets activated when any of the doors of the car is opened.
On each door a micro switch is fixed (if central locking is not already there). Once any
door is opened the switch of that door gets activated which in turn activates the alarm.
In some of the versions that are available in the market, the alarm will go on for 90 sec,
after which it will automatically stop. The advantage of such feature is that if the alarm
is unattended the battery does not get drained off. In some countries this is mandatory
that alarm must switch off automatically so that it does not endlessly disturb the
neighbors. Some of the systems offer additional protection upon activation like
cutting of the engine or cutting of the fuel supply etc.
Another type of automobile alarm gets activated when there is an impact on the car. Such
impact happens if someone breaks the glass or the car is physically towed away or someone
tries to open the door with force. The advantage of such a facility is apparent but there
are disadvantages too. One of the major disadvantage is that such alarms go off
accidentally even if someone leans on the car. Some of the systems are so sensitive that
if truck passes close by, the impact of the air can activate such an alarm. Such alarms
are quite cheap but lead to lot of false alarms and cause inconvenience to the owner and
the neighbors alike.
To overcome such disadvantages the advanced alarms use ultrasonic sensors. In such systems
the ultrasonic transmitters transmit the ultrasonic (high frequency sound waves) waves
which form a pattern in the car by getting reflected from various surfaces. The ultrasonic
receiver receives the ultrasonic rays indirectly after getting reflected from many
sources. If a door is opened or a glass is broken then this pattern of waves gets altered
and the receiver does not get the expected intensity of the ultrasonic waves. When such
change is detected the central unit then takes the predefined action which can be sounding
of alarm or cutting of the fuel supply etc.
Activation/Deactivation
To activate or deactivate the alarm there are two common
methods. First (the obsolete one) is the key pad based system in which owner has to key in
his password with in a specified time after getting in the car. Such a system is
inconvenient as switching on or off of the alarm requires certain time.
The second way to activate or deactivate the alarm is by using a remote control. The
remote is smaller than a match box and uses a predefined code while transmitting
information to Receiver. This code is unique for each car. Due to this unique code,
remotes from different cars do not interfere with each other. There are thousands (and
even millions) of such code combinations, depending upon the technology used by the Remote
manufacturer. The code is set by the manufacturer, in the hardware (IC) of transmitter and
Receiver. So, if you loose your Remote, you may not be able to get another one readily
from the dealer.
While the security systems are improving the thieves are also getting technology savvy. In
some advanced countries, the thieves use special equipment to decipher the electronic code
that the transmitter transmits to open or close the car. To beat this loophole, the more
advanced remotes use a hopping code. By using a hopping code the code is changed
automatically every time the remote is used . This system is useful to defeat thieves who
may use electronically advanced gadgets to track the codes.
In still advanced systems once the alarm is activated it activates a pager/beeper which is
carried by the owner. The range of such remotes is around 250 meters. The biggest
advantage of such pager based system is that user gets alerted every time the alarm is
activated in the car. Otherwise it has been seen that the alarms keep on going off in
parking areas, but the owners are unable to hear inside the house or in the office.
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