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Basically, a car alarm is nothing more than sensors connected to some sort of siren. Today's
car alarm systems include a few more features. These features include a radio receiver for
keyless entry, an extra battery so that the
car alarm will continue to operate even if the main battery is disconnected and a computer control unit, or brain, that monitors the
complete car security system and sounds the
car alarm if need be. The car alarm's brain is responsible for closing switches that activate
car alarm devices, such as your horn, headlights or an installed siren. Different sensors and how the different
car security components are wired to the brain differ among
car alarms.
Door Sensors
The most basic sensor of a car security system is the door sensor. Most
car alarm systems use the same mechanism responsible for turning on a vehicle's inside lights. Although door sensors are highly effective, there are other ways to enter a vehicle without opening a door, such as entering through a broke window or towing the car away. More
advanced car alarm systems will include additional sensors and will even monitor the vehicle's overall voltage. If the
car security system suspects the electrical system is being tampered with, the
car alarm will sound off.
Shock Sensors
Only cheap car alarm systems depend on door sensors alone. Higher
quality car security systems may include shock sensors. If a vehicle is moved in any way, the
intensity of the motion is sent to the brain. The car alarm then takes action based on the intensity of the motion.
Window Sensors
Most fully equipped car security systems include window sensors. A
car alarm system using Window sensors can detect broken windows either by the sound of breaking glass or by the change of air pressure in the vehicle.
Pressure Sensors
Even if the air pressure outside a vehicle and inside a vehicle is identical, when a window is broken or forced in, or if a door is opened, there is a change in the vehicle's air pressure. Some
car alarm systems will use this change in air pressure to trigger the
car's alarm. Pressure sensors still leave your
car security system useless if your vehicle is towed by a
thief.
Motion and Tilt Sensors
Perimeter scanners can be used by a car alarm system to monitor the
surrounding area of a vehicle. This is usually accomplished using a radar system. Some
vehicle security systems also include a tilt sensor. Using a series of mercury switches, the
car alarm can sense if a car is being lifted and how far.
Car Alarm Responses
Your car alarm system is pretty useless if it does not respond to an intrusion in some way.
Basic car alarm systems will use existing devices on a vehicle, such as honking the horn and flashing the headlights. More
advanced car security systems will cut off the gas supply, disable the ignition starter, or render the car undrivable in some other fashion.
Car alarm systems may also include a separate siren for producing
loud, piercing sounds, bringing attention to the car thief and hopefully running them off.
Car Alarm Remotes
Car security systems usually include car alarm
remotes, or transmitters, that can be added to a keychain for added convenience. These devices can be used to instruct the
car alarms brain remotely. Car alarm remotes can be used to instruct the
car alarm system to unlock your doors, turn on your headlights, or sound the alarm. Some
advanced car security systems have a pager system and a central computer that can be used to page your
transmitter when a vehicle has been tampered with. The
transmitter will even tell you which sensor was triggered and will allow you to disable the car.
Car alarm remotes use millions of pulse codes to securely transmit instructions. While this is fairly effective, it is not hack proof. Code-grabbers can be used to copy the transmitted key and then disarm an alarm. Rolling codes where developed to address this problem.
Car alarm systems using rolling codes will use a new series of codes every time the
car alarm is activated. Upon activation, the
car alarm's receiver creates and encrypts a new disarm code and sends it to your transmitter. The new disarm code will only be used once, therefore, duplicated codes are useless.
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