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Automotive Security Siren

My next question is about security.

My Maxima got broken into last week. They tried to steal the stereo, but failed. They did cause a couple hundred dollars in damage, though.

What I’d like to do is hook up an interior siren so that when the alarm sounds, the people breaking in get an earful. I was even thinking of an interior strobe light.

All I’d do is hook this up to the alarm system on the car so that when the alarm is sounding, the interior of the car is a very unpleasant place to be.

My car does not have a separate exterior alarm horn; it just uses the car horn.

Is what I’m talking about feasible for, say, $50?

If you do the work yourself, AND if your alarm has a siren output, sure, $50 would probably cover the cost of the siren.

In my MR2, I have a primary siren under the hood and a secondary one behind the radio aimed at the driver’s seat. Because I’m evil, I also have high-frequency piezo sirens (they’re quite small but loud as hell) mounted inside the headrests. They’re under the padding so you don’t see or feel them. I can report that the noise is not only unbelievably loud, but it’s actually somewhat disorienting.

That interior noise blast might actaully do something to deter thievery.
— Lord knows the honking horn crap goes unnoticed since there’s far too many parking lot noise makers numbing the public to any importance of them.

If you want to KNOW when someone’s there you need a pager type alarm.

Well, I’ve reviewed the wiring diagram for my Maxima (in the shop manual), and because this car has an integrated alarm system, I’ve figured out this would be pretty hard to implement.

In a nutshell, there are two paths to the horn relay; the first one comes from the horn switch, with grounds the relay and allows current to pass from the battery to the horn; the second is another relay, which is activated by the “body control module” – the second relay provides an alternate way to ground the first relay.

Conceptually, it’s not that hard to see how I could tap the wire that leads from the body control module to the security relay, but the problem is actually finding that wire. The manual does say what color it is, and which terminal number it is on the main wiring harness, and so forth. In concept, it’s not that hard to think of installing a wire tap to that wire – I even know what color it is. The hard part is getting to that wire.

I can get a piezoelectric horn from Radio Shack for under $10, and I have the wires and taps, etc. I just don’t have the courage to get into that wiring harness. So I guess for now, the answer is to just leave it alone.

Also, the activation wire from the body control unit pulses, so the interior siren would sound along at the same rhythm as the horn if I tap that wire.

On the bright side, the current draw on the piezoelectric siren is so low, I don’t think I’d need a relay to power it.