Car Alarm and Immobilizer

Posted on Feb 5, 2013

This circuit features exit and entry delays, an instant alarm zone, an intermittent siren output and automatic reset. By adding external relays you can immobilize the vehicle and flash the lights. One of the inputs is connected to the vehicle`s existing door-switches. This provides the necessary exit and entry delays. It`s usually sufficient to connect a SINGLE wire to just ONE of the door switches - they`re generally all connected in parallel with the return through the chassis. You can add extra normally-open switches to the door-circuit if you wish; but note that any additional switches will have to be able to carry the current required by your vehicle`s interior light.

Car Alarm and Immobilizer
Click here to download the full size of the above Circuit.

The alarm is "set" by opening Sw1. It can be any small 1-amp single-pole change-over switch - but for added security you could use a key-switch. Once Sw1 is opened you have about 10 to 15 seconds to get out of the vehicle and close the door behi

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