If you are considering a car alarm system for your vehicle, then here is some information that will help you choose the best one. Choosing an alarm system can be a scary thing, since there are so many choices available and most car audio clerks work on some sort of commission and will try to hard sell you on certain brands or models.

It is important to remember that certain car alarm systems are not compatible with certain vehicles. Check your owners manual to find out what can be installed, or talk to an installation expert.  Also, while your looking up compatibility, find out if your vehicle already has a pre-installed alarm system. Some newer cars do, and they may be set to the default OFF position.  If your car already has an alarm pre-installed you can use that one, or upgrade it if you want more features.  This will need to be done by an installation professional however.

There are two main types of alarm systems for your car: alarm systems that you arm with a remote, sometimes called active systems, and alarm systems that arm automatically when you exit the vehicle, also called passive systems.  An active alarm system will arm after you press the button, and the car will alert you with an audible sound, likely the same sound that you hear when you lock your car remotely.  

A passive alarm will arm a certain number of seconds after a door is closed, to make sure it is the last door closing. Often, these types of alarms will get you a discount on insurance, especially if you have comprehensive insurance that covers you if your car is damaged during a theft. 

After figuring out which systems are compatible with your vehicle, it's time to decide on what features you want. Get a piece of paper and make a list. Categorize your features into three sections, what you can't live without and what you can live without, but would like to have, and finally, features that you could care less about. This will help you determine if the price of a certain feature is worth it, as certain features make the price go up considerably. Below is a list of features that you can get with car alarm systems.

Re-Arm: This feature re-arms the car alarm after a certain period of time if it does not detect a door opening. That way, if you accidentally disarm the alarm from the remote, it will re-arm itself before someone has a chance to take advantage of your error.

Air Horn System: This is a much louder sound than the regular alarm, and it blasts from within your car, meaning that the thief will have an extremely hard time concentrating to try and steal your car, and more attention will be called to your car.

Code Rotation: This feature changes the alarm code each time the system is armed or disarmed. This means that your code cannot be picked up by electronic surveillance and used to disarm your car alarm system.

Anti-Carjacking: How this system works is by shutting off the engine and emitting a loud siren if someone attempts to take your car by force. To disable the system, you must have the remote and know where the hidden switch is, to press both simultaneously in most cases.

Dome Light Notification: This feature turns your dome light on when you alarm is disarmed, to remind you to arm it.

Flashing Lights: This features causes some of the vehicle's lights to flash when the alarm goes off, illuminating the car in a dark parking lot. Generally, the lights will also flash when the alarm is armed or disarmed as well, as an additional confirmation to the audible notification.

LED Warning: A blinking light in the interior of cars to warn would-be thieves of the presence of an alarm system.

Pager: This will send a signal to you, on the included pager, when the alarm is activated.

Remote Start: A feature that allows you to remote start your vehicle from the remote. You also generally get remote lock/unlock with this feature.

Tracking Device: If the alarm system does not deter a thief and your vehicle is stolen, this feature allows you and police to track your vehicle via GPS, which will enable police to catch the thief quickly, before any damage is done to your car.

Trunk Release: This will allow you to open your trunk from the remote, which is extremely useful if you have your hands full.

Don't put a sticker from the manufacturer on your car. These are notices to thieves that there is something valuable inside the car, or that the car itself is valuable and you may attract a thief by just driving along in traffic.  

Don't show off your speakers and bass as you drive around.  Keep your music down low, and don't advertise that you have an expensive stereo system.

Get a passive system for your car.  No matter how well you remember stuff, the fact is that humans are busy and forgetful.  The one time you forget to arm your system is the one time it could be broken into. Computers never forget, so let the computer do the arming for you.

Park as close to the store as you can, or find a light to park under.  Generally, car thieves will not want to do their work out in the open, near people, or in a illuminated area.

Adding on custom grills, rims and spoilers is an advertisement that you have tricked out your car, and is an invitation to thieves.  Keep your add-ons out of sight if possible.  

Car Alarm System prices vary considerably, but you can almost always get one that does everything you'll need it to, for between $100 and $200.  If you want added features such as the ones above you may end up paying a bit more, but I don't recommend spending any less than $100 on an alarm system, even though there are El Cheapos that you can get for next to nothing.  Remember: You get what you pay for.