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Alarms and Safety Systems

Alarms and safety systems are indispensable accessories for many conscientious car-owners.

Alarms and Safety Systems

Choosing from the many available car alarms and safety systems can be a daunting but necessary task. According to the FBI's Uniform Crime Reports, a motor vehicle is stolen in the United States every 26.4 seconds. Car owners who would like to keep their automobiles from becoming a statistic have a wide variety of alarms and safety systems available to them.

Door Sensors

Of all the available car alarms and safety systems, a door sensor is the most basic. A programmed door sensor goes off any time the hood, trunk or any door on a protected car is opened. Door sensors operate on the same pre-wired circuit that turns on the inside lights when a door or the trunk is opened. Some modern alarm systems can also measure varying degrees of voltage and can recognize if someone has interfered with the car's electrical system.

Door sensors are popular because they're basic and easy to use and install. Unfortunately, they have limitations that restrict their ability to fully protect a car. For example, a door sensor won't go off if a thief breaks in through a window. A door sensor also offers no protection if the thief manages to tow away the car without actually breaking into it.

Shock Sensors

Since door sensors have such severe limitations, most advanced car alarms and safety systems use shock sensors. A shock sensor will go off if a protected car is hit, jostled or otherwise moved.

The most basic shock sensors are configured by placing two flexible metal contacts by each other. When the car is moved or jostled, the two contacts touch briefly and complete a circuit, setting off the alarm. The main problem with these basic shock sensors is that the alarm has no way of measuring the intensity of the jolt, so it sets off many false alarms.

Advanced models of shock sensors attempt to correct the problem of measuring intensity. These shock sensors consist of a central electrical circuit in a cylindrical housing, a few smaller electrical contacts at the bottom of the cylinder and a metal ball that moves around freely inside the cylinder. When the car is moved, the ball rolls around inside the cylinder and completes the circuit. These models allow the car to measure the intensity of the jolt. For example, a small bump may only cause the ball to roll from one electrical contact to the next. In this case, the alarm may not even go off at all. But if the car moves, causing the ball to roll a greater distance, the alarm will sound.

Window Sensors and Pressure Sensors

Car thieves often think the easiest way to break into a car is to smash the window, according to Essortment. For this reason, it is a good idea to get a safety system that includes window sensors and pressure sensors. These alarms will go off if a thief attempts to steal a car by breaking a window. A window sensor is usually just a microphone connected to the car's brain. The sound of breaking glass has its own unique frequency, and the sensor will pick up on that and sound the alarm.

Pressure sensors offer an additional level of protection. They measure the normal air pressure in the car. The act of someone breaking a window or opening a door briefly alters the air pressure in the car, setting off the alarm. Pressure sensors are often built into a car's stereo speakers, but they may also be manufactured separately.

Tilt Sensors

All the door sensors, window sensors and pressure sensors in the world won't help an owner whose car is simply towed away. Some thieves don't intend to drive the car but instead break it down for its parts. In that case, they won't bother trying to break in; they'll just carry it away.

Several alarms can protect against this kind of theft. One kind is a perimeter scanner, which uses basic radar to monitor the area immediately surrounding the car.

Another alarm that protects against towing thefts is a tilt sensor. Tilt detectors are made up of switches that contain mercury. When a protected car is tilted, for example, if it's hooked up to a tow truck, the mercury flows downwards and completes the circuit that triggers the alarm. Since motion and tilt sensors only protect against a very specific type of theft, they are best used in combination with other alarms and safety systems.

The biggest drawback to any car alarm is the number of false alarms, when the alarm is triggered by something that's not actually a break-in. People have gotten so used to hearing car alarms that they sometimes don't pay attention to them.

Car thieves are always finding new ways to get around car alarms and safety systems. Even with the drawbacks, however, the best safety system is a combination of multiple sensors. A car equipped with door sensors, shock sensors and motion or tilt sensors is much more secure than a car with only one of these systems.

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