DayCare Van Alarm Buzzer w/Relays

I'm supposed to be designing a functional alarm to install in daycare vans for my work, and I'm having a little trouble. I'm trying to use the smallest amount of relays while not leaving any energized while the vehicle is off. What I need is a setup that energizes a buzzer when the ignition is turned off, and that buzzer is subsequently turned off when the driver crawls to the back of the van and pushes a momentary pulse type switch. In most of the vans I work with the ignition wire switches from 12v to ground when the car is turned off, I'm wondering if this can be used to make the setup more compact. Any help would be greatly appreciated.

that would be a rather simple project. extremely simple, in fact.

soundmasta wrote:

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that would be a rather simple project. extremely simple, in fact.

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Would you like to elaborate on this? I can come up with a couple designs later if no one else does.

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Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

I'd appreciate any ideas, besides just how simple it would be to make. I figured it would be simple, but it seems like I have a blindspot to this project. Thanks.

Alright, here is one idea. I didn't test it but it should work. The only thing not listed is the ground for the buzzer/siren. Ground that to the actual ign wire before any of the diodes in the diagram.



PS this will cause the buzzer to go off whenever the ign is turned on then turned off. You will then have to hit the momentary switch to shut it off.

PSS, I am waiting to be shown up here.

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Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

It looks like it should work fine. I've never used the ground signal of a turned off ignition wire to ground anything before, that's where my blind spot was with this. To the best of your knowledge do most ignition wires function this way? Thanks for pointing me in the right direction, this is how I imagined it should have worked, but it just wouldn't click. I'll put it together on the bench Monday, and I'll let you know how it works. Once again thanks.

Works just how it should on the bench. Now I just got to put it in the first customer car. Thanks.