A car alarm is a device installed in a vehicle to discourage theft of the car or its contents. When the alarm is triggered, emits a loud annoying siren or klaxon or the vehicle's own horn to alert passers-by or the owner that a theft is taking place. Some car alarms installed will flash some of the vehicle's lights or notifying the owner via a paging system as well as interrupting electrical circuits necessary to start the vehicle.

A car alarm can be divided into two categories: the OEM or Original Equipment Manufacturer (built into the vehicle at the factory) and Aftermarket (installed at a later time after the car has been built).

An OEM car alarm is made by the same manufacturer and is the original device installed when building and selling the product. Some OEM car alarms in the market often have indications such as meets OEM standards. These devices are not OEM; they are simply made to the same specifications as the OEM parts.

On the other hand, an Aftermarket car alarm is provided by dealers and car parts stores to customers and installed to the vehicle as a replacement or upgrade of the original device.

Car alarms in most cars these days are armed and disarmed using the vehicle's keyless entry remote. However, on many vehicles the key cylinders in the driver or front passenger doors activate switches, so that when a key is used on a door the alarm will arm or disarm

Aftermarket alarms are usually armed and disarmed via remote.

When the conditions necessary are met to trigger the alarm, the car will emit high frequency sound to discourage theft. However, because its sensitivity and since car alarms are usually triggered accidentally, car alarms are often ignored by people.
False car alarms occur because the car owners use high sensitivity settings. Another reason is that the car alarm is not properly installed into the vehicle. The shock sensor of the device can also be mounted on a surface where there are usually vibrations.
Some car alarms these days no longer emit a high frequency sound. Instead, they inform the owner via a paging system. Some car alarms are installed with GPS so that authorities can locate the stolen vehicle.

The Australian Automotive Aftermarket Association (AAAA) is the peak body that is concerned with the manufacturing, re-manufacturing, wholesaling, distribution and retailing of all vehicle parts, accessories, tools, equipment and services.

Tips when buying car parts

• Know all the details of the parts that you need for you vehicle and compare them to each other in order to realize their suitability for you. Some accessories might not be compatible with your car and might not produce the desired change.
• Choose the right car parts store. Reputable and trusted dealers often have good track records and are recognized by the AAAA.
• Ask family and colleagues for any recommendations.
• Check all the parts for any damage before purchasing them and do not be afraid to ask questions every time.
• Car parts stores should always have their policies posted and should be able to address all your concerns and queries to your satisfaction.