There are many different types of alarms, ranging from the 2-wire voltage sensing hook up, to the high-end alarm that will unlock your doors, roll up windows, pop your trunk, even start your car by remote. There are even some alarms that will hook up to cellular phones, so that you can start your car or roll up your windows when you are in the Bahamas. A alarm can do anything you can think of, limited by the installer’s skill and imagination.
The siren is the most important part of the alarm. It is what deters most thieves. The common multi-tone siren is usually not enough, since most people do not pay attention to them. Adding additional horns, airhorns, etc to call a lot of attention is a good idea.
The starter disable won’t stop anyone from stealing your stereo, but it will hopefully stop or slow down somebody that wants to take the car. Bypassing starter disable circuits is very easy for an experienced thief. Keep in mind that if somebody wants to really take your car, they will.
LEDs are the only thing that lets a thief know that there is an alarm in the car, hopefully making him reconsider into moving on to the next car. LEDs should be bright and in a highly visible place.
Valet switches should be concealed, but easily accessible. These are used mainly in case of emergency, when a remote control does not work and the alarm needs to be turned off.
Door switches and hood/ trunk switches are the most reliable way to detect a break in. Since sensors sometimes fail or are improperly adjusted, switches must be hooked up, even on voltage-sensing alarms.
When the alarm is turned off, the dome light lights up the interior of the car for a predetermined amount of time (usually 3o seconds, or until the key is turned on.
Proper mounting and adjustment are critical to a security system’s performance.
Shock Sensors: Shock sensors are mostly electronic, and are made up of a crystal that produces a small voltage when vibrated. The sensor then amplifies the signal and sends it to the alarm. An older type of shock sensor is mechanical and consists of a metal contact in a spring. When the car vibrates, a metal attached to the end of a spring makes contact, setting the alarm off. Newer alarms have a 2-stage sock sensor, that has two outputs: One that triggers the alarm after a hard hit, and the second that either goes to a pre-warning input on the alarm, or hooks up to the siren. This second stage is more sensitive than the first stage, and it gives a warning if for example somebody hits your car when opening their door. If they hit the car harder then the alarm will go off.
Microwave Sensors: Most commonly used on Jeep Wranglers and convertibles. Also called perimeter, proximity or radar sensors, they emit a harmless field of microwaves. If that field is disturbed by a physical object, say a hand (not wind or a leaf), then the alarm goes off. As shock sensors, there are 1 and 2 zone microwave sensors. The second field is used to warn people to get away from the car when they get too close either by a synthesized voice, or by beeps, while the first field makes alarm go off only if something is in the car. Ideal location is in the center of the car, under center console (as long as not obstructed by metal objects).
Glass Breakage Sensors: These sensors use a tiny microphone to “hear” high frequency sounds. Usually the unit is installed under the dash, with a microphone sticking out either under the dash, or console. If not properly adjusted, rain will set them off.
Motion Sensors: Most use a pendulum with a metal contact at the end, or mercury switches(older). They are usually not so reliable, and are not really necessary, unless you are willing to have false alarms every once in a while to try to protect outside of car.
By interfacing an alarm with factory or aftermarket door locks, you will never need to use the key again to get in the car. Many alarms automatically lock the doors when the ignition is turned on and unlock when off. Some alarms offer two-stage unlocking: Push the disarm button once, and it only unlocks the driver’s door. Push it twice and it unlocks all the doors.
This feature enables you to activate a factory or aftermarket trunk opener via your alarm’s remote control. Really handy feature when going to the supermarket.
Many accessories can be interfaced with an alarm, such as window roll-up modules, remote car starters, garage door openers, turn a radio on and off, motorized amplifier racks, etc.