Install a Car Alarm

Most do-it-yourself car alarms are simple devices that provide minimal security. If you don't want the hassle of installing the alarm yourself, look for an automobile alarm and security company that will do the job.

Connect your car horn to your car alarm

Parts: 1. diode 2.normally close relays.
Step 1. Connect the positive of the diode to the positive wire of the siren.
Step 2. Tap the orange alarm wire, which is then connected to pin 85 of 1st relay, pin 86 of the relay is connected to the negative of the diode. Pin 30 is connected with a constant 12 volt, pin 87 is connected to pin 86 of the 2nd relay.
Step 3. Locate the black/white domelight output of the alarm and connect it to pin 85 of the 2nd relay.
Step 4. Pin 30 of the 2nd relay is connected to a constant 12 volt and pin 87 is connected to the positive of the car horn. Only when the alarm is triggered will the car horn honk.

Go discreet with wiring

The first thing a professional thief will do is pop the hood. If he sees a siren or a wire loom that looks out of place, he will cut the wires and your alarm is done. Hide those wires, hide that siren, make him think for a second. Make it so he has to pull the cable off the positive terminal to make the thing shut off.

Keep your alarm going for as long as possible. A backup battery and a 2 way paging system may help if you live in a higher crime area.

Go basic

Car alarms have many fancy detectors. If this is your first time installing a car alarm you will realize it's a very tedious process. Just do the basics. Find your door switch wire (only a positive or a negative detection wire is required), and install the shock sensor. If you want a glass breakage sensor or a radar sensor, wait till later. Just get started and see if you can tough it out.

Locations

If you are new to installing car alarms, you probably have noticed there is no specific manual to installing them for your car. Location is critical. Out of sight, yet not out of sound, shock or view. The easiest place for me to start was directly behind the battery and beyond.
The main unit goes greatly in most cars behind the glove box. Most factory installers put it on the drivers side. Running wires to the drivers side is quite easy and not too pricey. The trick is to keep the system on (especially if you have a paging system) and to think like a criminal (how is it possible to break into my own car).
Keep your sensors in locations that define what your sensor will detect. For example, Shock sensor. Mount it directly on a piece of metal inside the car. Don't even use double sided stick tape. Duct tape that bad boy on plastic to metal. You can always lower the sensitivity (or put some thick tape on) afterward if it goes off when you start your lawn mower.

The previous owner of my car had a factory guy do it, he put the shock sensor on the plastic steering wheel shaft and got his car stolen. Now that I've installed it, it does what it's supposed to do. Punch any part of the metal and it will trigger.

The glass breakage sensor would logically need to be located around glass that would break. Any small windows in the car, preferably on the drivers side, would be best. It detects a certain frequency.

Use your own judgment, you can do it. There is no reason to pay $100 an hour to have a foreign system installed in your car when you can do it yourself for free and gain knowledge and experience.

Voltmeter vs. test light

On vehicles with airbags, ALWAYS use a voltmeter to test wires. NEVER use a test light! The current draw from a test light is enough to trigger the airbags if you probe the wrong wire.