Vehicle Immobilizer




Simple, robust, touch sensitive electronic switch which can prevent vehicle theft even if thief has vehicles keys - see testimonials below....

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Step 1: Preparation

Gather together the necessary components, materials and tools.... the images below show the necessary electronic and mechanical components - you'll also need some epoxy resin (about 5ml), some lacquer, solder and a few tools - more information can be found on my website -

Step 2: Assembly

Assemble the components according to my slightly antiquated and long winded animated instructions written for electronics students - if it is not easily viewed on your display, it may also be viewed here

Step 3: Test Your G-Spot

Apply +ve power to the anode of the SCR, connect a load to the SCR's cathode and then earth the load... now touch the G-Spot as well as earth at the same time and the load should operate... see schematic below....

Step 4: Install Your G-Spot

Pop the vehicles hood/bonnet or boot/trunk.  Locate the battery and follow the largest cable from the batteries +ve terminal to the vehicles starting solenoid.   Disconnect one wire at a time (if more than one) from the starting solenoid until turning the key doesn't start vehicle.  This is the wire you need to interrupt with your G-Spot so trace it to a point where it is far enough away from the engine heat and cut it - it can be under the hood/bonnet or under the dash in the passenger compartment.  The end of your G-Spot with the wire coming from it (Anode of SCR) connects to the end coming from the ignition key, the other end (Cathode) connects to the end going to the starting solenoid.  Crimp your G-Spot in place and then run the sensing wire to a screw or other conductive spot within easy reach of the driver - this must be isolated from the vehicles earth!  Test your installation by turning the key to "Start" while simultaneously touching the vehicles G-Spot.  Note:  You must be earthed while doing this so if your keys are plastic coated you may have to slide a finger down onto the barrell of the ignition (usually earthed) or get an uncoated key cut.  If it doesn't work and you're sure you're earthed, etc, try giving your fingers a lick otherwise a separate relay may need to be fitted due to the small voltage drop across the SCR.  Casually check to ensure no one else is watching before operating any G-Spot!  For more information see -

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    10 Discussions


    7 years ago on Introduction

    I think this is a great idea. It would be even greater if the instructions were clearer. Maybe if the instructions were broken down into more steps and step by step photos including car installation... Perhaps add links for the parts. Make it simpler for non electrical folk who like to tinker. Thanks.


    9 years ago on Introduction

    I am utterly confused. Are the only instructions inside your GIF, which leaves no possibility to pause, rewind, or fast forward. If you miss a step, the only thing you can do is restart the animation and watch the entire thing again. Is there a step by step part with photos that I am missing? I really want to make one, but your directions are the only ones I have found. After I started to watch the animation three times, I am afraid that I am going to miss something. It seems like a great idea, but I just can't follow it that fast. I am afraid to make one with the sole direction of that animation. Is there standard (i.e. a page of step by step) directions anywhere? All I can find is the YouTube video, which seems to be a different version.

    4 replies

    Reply 9 years ago on Introduction

    hi whosdadog - this and the YouTube are the only versions that I'm aware of. Yes, the YouTube version is different - it uses leaded components - not SMD's - and there is no PCB or diode used. Maybe you could try capturing a few screen-shot's of the animation - the PCB image is probably the most important part. Hope that you manage to work it out.


    Reply 9 years ago on Introduction

    Yeah, I tried to get the frames out of the gif, but PS would cooperate. The most confusing part is when the gif is showing to how to lay out the components. Its hard to tell what is supposed to connect to what. I'll have to try to get the frames out some other way. Thanks