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How do I make an alarm go off when a person touches my car?

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david90

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How do I make an alarm go off when a person touches my car? I'm thinking of using a capacitance switch or something that can switch on an alarm.
 

david90

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car touch alarm circuit

so can the touch plate can be connected to the car's frame and it would activate the alarm when a person touches the car at any spot? Do I need more than one for different section of the car?
 

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XNOX_Rambo

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touch alarms car

Well, as long as the sections are galvanically connected to each other (most
likely) you will only need one connection spot.
Of course, if your car is e.g. a Corvette with a fibreglass body it won't work.

Be aware that you need a separate battery for the alarm, as the negative pole
of a car battery is connected to the chassis/body.
 

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david90

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proximity alarm car

is there another way around using a differnt power source?
 

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XNOX_Rambo

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car:s body touch alarm

You could build a switched, isolated power supply for the circuit.

But I have my doubts that the circuit would work anyway as I am not clear on
its principle. Either it could be utilising the mains hum, which is picked up by our
bodies, but then it would only work in the presence of mains wiring.
Or it could use a charge transfer from the body to the touch plate - in which case
I believe the body of a car would be too big of a "plate", distributing the charge
over a large area. The example calls for a door knob as the touch plate,
which presumably gives a better effect.

So, back to the drawing board... :wink:
 

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david90

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car touch alaram

I walked by a car today without touching it and the siren started to beep. How does that work?
 

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