This article is submitted by one of our readers: Dan Davies

All the content and  photographs used in this article has been sent to us by Dan. He told us this would be a good project idea for the readers of CircuitsToday and we also think alike. Thanks Dan Davies for your kindness to share this project and the interest you are showing to grow this community. Please share your thoughts as comments.

Electronic Vehicle Immobilizer


This simple vehicle immobilizer circuit is cheap, easy to make, install and operate . It’s also very discreet.

Thoroughly field tested, it’s robust and weather resistant design can prevent vehicle theft even if the thief has the keys!

In it’s most common application, it prevents the engine from turning over until the vehicles ‘G-Spot‘ is touched at the same time the key is turned to the ‘Start’ position, and the operator is earthed!

Here’s a completed G-Spot beside an AA battery:

Animated Schematic and Circuit Description

I know, it’s a little bit ‘fancy’:

Turning the vehicles key supplys power (red).
The SCR prevents operation of the load until the voltage on the base of the PNP transistor is lowered by the earthed owner contacting the G-Spot (green),
This turns the transistor on and current then flows through the collector circuit and 220 ohm resistor (orange), triggering the gate of the SCR.
Once triggered, the SCR allows power to flow to load (green) and remains on until power is isolated.

Parts and Materials

These are all the electronic components required ~ the diode is not essential:

These are all the mechanical components:

You’ll also need a small amount of:

Solder, cleaner, tape, lacquer, fiberglass resin and hardener.

Assembly and Basic Installation Instructions

Here we show the construction of a similar product which uses leaded components,can be watched on this YouTube video:



  1. it is gud !!! but need more details to finish up

  2. jojo

    Hi Edgardo,

    You may check the link now. I corrected it!