add 2 sirens to existing oem alarm

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axel_ny

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Joined: March 26, 2008

Location: Texas, United States

Posted: March 26, 2008 at 9:08 PM / IP Logged

i plan to remove the stock horn from the alarm of an 01 audi a6 and add 2 mini pazo sirens but i wonder if i need any relay there and how i should wire it to the existing alarm horn supply. and also what diferance would made if i add an relay instead to just wire straight to the horn terminals? and do i have to run any extra wires , or using just the 2 wires from existing horn are enough , sorry if i repeat any topic, thank you!

tedmond

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Posted: March 27, 2008 at 10:08 AM / IP Logged

you would use relays for sure. Connecting sirens to a horn ouput will burn if not fry your cars electrical system. the thing is, factory alarms are wired straight to horn, if you were to connect the honrouput to a relay, when using the horn honk, your piezos will go on as well. you could possibl break the continity on the horn wire and make it work with the piezos only - but piezos are meant to be inside a car, not out.

KPierson

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Posted: March 27, 2008 at 10:37 AM / IP Logged

I don't think you would need relays. The OEM horns should be already powered by a relay (you may want to check your service manual for verification). Typical OEM horns use low current switches on the steering wheel to power a relay that powers the horn. I can't imagine two piezo sirens using more current then the OEM horn.

It sounds like you are removing the horn all together, you may want to check in to the DOT regulations for a working horn and how loud it needs to be. I am not sure you can legally replace an OEM car horn with a piezo siren.

Kevin Pierson

axel_ny

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Joined: March 26, 2008

Location: Texas, United States

Posted: March 27, 2008 at 5:44 PM / IP Logged

01 audi a6 , my car has 2 horns one under the hood with switch is in the steerwheel for "driving " and another one is separate and in another circuit , in the trunk and is supply by the alarm when is trigger , what i wanna do is to remove for good the horn from the trunk and add in that line 2 piezo sirens , and my question is do i need any relay , what kind and what`s the diagram for it and if i don`t need a relay may i just simple add them to the existing wires coming from alarm, where was the old alarm horn?

KPierson

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Posted: March 27, 2008 at 6:14 PM / IP Logged

I see, that makes a bit more sense. It's hard to say if you can hook it up direct, you will need to figure out how much current the piezo will draw and compare that to the current draw of the horn. I would guess that you won't need a relay or anything but it is hard to say.

What kind of horn is it? Is it an actual horn (one loud deep tone) or is it more of a siren that changes frequency? If it changes frequency it may be possible that the alarm drives it with a audio signal, not a straight 12vdc voltage (I've seen that in the Honda and Acuras).

For specific vehicle information like this you may be better off asking this question on an Audi forum. Most installers won't get that deep in to the car!

Kevin Pierson

axel_ny

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Joined: March 26, 2008

Location: Texas, United States

Posted: March 27, 2008 at 11:23 PM / IP Logged

the horn i have now is like a regular horn , doesn`t change the tone or frequency when is activated, on audi forum are people who replace whit one and no problem , but i wonder if i add two if it will made any difference in wireing. i will test too see how much volts i have for old horn , but i can bet is straight 12v. some people say i need relay so that will activate the siren ...i will end up made the circuit and tested before take the car apart to hide the sirens.... but yes any advice would help , thank you!!

Chris Luongo

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Posted: March 29, 2008 at 8:46 AM / IP Logged

I also don't think you would need a relay.

I think I know the horn you're talking about. It sounds a little bit different from the horn you use for driving, but it's pretty much the same thing, right?

That kind of horn draws a lot of current, and should already be powered up by a relay from the factory. You should be fine to disconnect it and wire in aftermarket siren(s). Two sirens should be OK.

Obviously, if you were going to hook up a dozen aftermarket sirens, or a high-powered police siren or something like that, the stock system probably wouldn't provide enough power, and you'd want to use a separate relay.

Also:

--It would be best to just unplug the stock horn, and splice into its wire (without cutting the plug off). This way, it's easy for you (or the next owner) to switch the car back to original if desired.

--Most six-tone sirens that come with aftermarket alarms are meant to have steady power going to them, and they go through their six tones over time.

I would imagine your Audi's alarm system pulses the horn on and off repeatedly. If you connect a siren to that, you'll just hear the first tone, over and over again.

--If you said you were putting in those small piezo sirens, they only have one tone, so that part won't matter.

axel_ny

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Joined: March 26, 2008

Location: Texas, United States

Posted: April 02, 2008 at 4:53 PM / IP Logged

ok.... do i need or not a relay , i already put the 2 extra sirens insted of the original alarm horn (the one ddicated for alarm not the "driveing one") the original horn was supply with 9v and 2v to get the alarm tone, my 2 xtra sirens work , but i wonder if i can gain more power (lauder sirens) if i add relays and how i should connect them. thank you!

KPierson

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Posted: April 02, 2008 at 6:46 PM / IP Logged

A relay won't trigger off of 2v, and may not trigger off of 9v. You're best bet at that point is to use a transistor, something like a 2n3904. Use a 220 ohm resistor between the base of the transistor and your signal. Ground the emitter, and then run the output of the collector through a 22 ohm 1/4 watt resistor to the (-) side of either the sirens or a relay. You, at this point, really need to know how much current each piezo will draw, as the current will determine if you need a relay or not, NOT the voltage.

Kevin Pierson

KPierson

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Posted: April 02, 2008 at 8:38 PM / IP Logged

I have a piezo sitting here and I just did a current measurement on it - roughly 0.250A at 12vdc. Two of them should be around 500mA.

Kevin Pierson

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add 2 sirens to existing oem alarm

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