using a relay to back up if siren is cut
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=112270
Printed Date: October 31, 2024 at 7:04 PM
Topic: using a relay to back up if siren is cut
Posted By: 88transamfreak
Subject: using a relay to back up if siren is cut
Date Posted: March 11, 2009 at 12:08 PM
Back in the 90's when I started in car Audio I was reading a magazine where a guy installed a security system for competition (secuity system competition was big then) He installed some relays to sound a back-up siren / horn if the main siren was yanked out or the wires were cut. I thought this was a pretty cool feature but can't get a grasp on how this might have been done. I wouldn't mind doing something like this in my Firebird and hid a siren in the rear somewhere, only to come on if the main one was disabled. Anybody have any ideas? There has to be a way to do this? Thanks! ------------- 1976 Camaro
1982 Corvette
Replies:
Posted By: 88transamfreak
Date Posted: March 11, 2009 at 12:23 PM
Ok, I've thought about this, I should be able to take a relay and supply either a positve or negative signal to it and when that signal is severed (ie; someone yanking the main siren out or cutting wires)..it cause the relay to supply a ground to the negative of the second sire and cause it to emit sound. The only way I can see this working is to solder a 2nd wire (to either ground or positive) on the main siren up REALLY close to the base and the act of cutting the wires will also sever the "special" wire going to the 2nd siren and doing what I mentioned above. I hope this makes sense ------------- 1976 Camaro
1982 Corvette
Posted By: Thack79
Date Posted: March 11, 2009 at 4:23 PM
Just mount the siren against the firewall and and be creative in you wiring (i.e.within the factory car loom). Dont seem like its really worth the time and effort. If im able to get under the hood, Ill just undo the whole battery cable. Some people use a backup battery DEI 520.
Posted By: 88transamfreak
Date Posted: March 11, 2009 at 4:46 PM
Thanks for the reply, I have that battery back-up and the siren has a battery back-up built on it as well.
I thought about buying a electronic hood lock to lock the hood, instead of trying to figure out the siren deal.
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1976 Camaro
1982 Corvette
Posted By: dualsport
Date Posted: March 14, 2009 at 10:59 AM
It could be done pretty easily by adding a monitor for the connection on the siren, using a solid state inverter. You can't use relays because they'll draw too much power on standby.
Just needs a high resistance pullup on the line you're monitoring, so that it'll go high when someone disconnects the siren. Normally the connection keeps the voltage at zero because the pullup is very light, keeping the backup turned off.
If the line is cut, the inverter will then turn on and drive your backup siren.
A simple transistor and one resistor would do it. Use the output to drive a relay if you need more drive current for your siren.
You could even rig it up to monitor the battery so if someone disconnects the battery it'll sound off (assuming you're using a backup battery)
Posted By: howie ll
Date Posted: March 14, 2009 at 2:27 PM
If you have a back-up battery siren already, cutting the wires will trigger the siren's internal batteries anyway, at this point they've opened the hood, and have your engine bay at their mercy, it's already too late, I'd simply have wired that back-up battery INSIDE the car with your secondary horn to factory horns, another siren or airhorns.
Posted By: Mike M2
Date Posted: March 14, 2009 at 3:42 PM
Back in the 80's when Alpine first started making alarms, they came with a siren with three wires. One was ground, one 12volts and one negative to the alarm itself. If for any reason the alarm was disconnected or the wire to it severed the siren would sound. I haven't seen sirens like this in over 20 years but i really liked the idea if someone found the brain and unplugged it 120DB of siren would be blasting...
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Mike M2
Tech Manager
CS Dealer Services
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