Simple Car Burglar Alarm Circuit

Why a Burglar Alarm is Necessary in Cars

How important is your car to you? Well, you may say that’s a ridiculous question, off-course a car is too important for any individual.

In fact it’s like a home to many and an indispensable part of life.

Truly, a car is quite comparable to a house as today it is perfectly equipped with comforts equivalent to that present in a house.

Take for example, a music system – probably, the one that may be installed in your car is much sophisticated than the one situated in your home.

Hmm….but did you know that if it’s so valuable to you, it can also be to many other eyes….constantly hovering around vehicles to grab and run off with one your most valued gadget.

Yes we are talking about burglars especially trained for robbing expensive car accessories too softly and swiftly for anyone to notice.

Before you feel too enlightened and head for the market to get a security system installed in your car, I would like you to give it a rethink - regarding a simple 1 dollar electronic car burglar alarm circuit idea that would provide the same level of security to your car audio or any interior accessories for that matter as an expensive $100 system would offer.

Let’s read the following discussion to know regarding its circuit description:

How this Simple Burglar Alarm is Designed to Work

We know that normally the body or the metal chassis of any vehicle is kept at ground potential and is done by connecting the negative of the battery to the body of the vehicle.

Thus it acts like a huge ground or “earth” and helps to absorb all electrical interferences. This particularly helps the audio systems to produce clean outputs.

Moreover this also provides an easy and short access to all electrical gadgets to the negative line as their negative contact can be directly fixed to ground avoiding cumbersome wiring. The above grounding feature proves to be an effective pick-up point for the present circuit.

Basically, a trigger point from the circuit is attached to one of the fitting bolts of the car audio system. As long as this point of the circuit is held at the ground potential everything remains normal.

However, if a burglar tries to uninstall the system and detaches the bolt, the circuit fires and sounds the car horn alarming everybody around, and you of a possible theft.

The circuit of a car burglar alarm system shown alongside is brutally simple and easy to understand. Transistors T1 and T2 are configured as current amplifiers.

As long as the junction of C1 and R1 is held at a ground potential (as explained above) T1 is inhibited from conducting.

However the moment this connection gets disconnected from the ground potential, positive voltage gushes in through C1 and triggers T1 into conduction.

This immediately charges C2 and also triggers T2 which ultimately sounds the horn and the alarm.

C1 makes it sure that T1 is allowed to conduct only for a second, which happens to charge C2 fully. C2 along with R2 and R3 forms a kind of a short duration timer and keeps the horn active for a few seconds, enough to rattle the burglar and make him flee forever.