Good idea or bad? Adding sensor to factory alarm
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=65267
Printed Date: September 13, 2025 at 10:07 AM
Topic: Good idea or bad? Adding sensor to factory alarm
Posted By: techfiftyfive
Subject: Good idea or bad? Adding sensor to factory alarm
Date Posted: October 29, 2005 at 10:39 PM
I have a glass breakage sensor that I want to add on to my factory alarm. Since there isnt an on/off switch (Yes, I know I could make one but I dont want to), would it be a good idea to use my ignition wire as ground? If not, anyone else have any idea's?
Replies:
Posted By: dualsport
Date Posted: October 29, 2005 at 11:05 PM
Probably would be okay since it draws very little current, but if you just want it to be powered up whenever you shut off the ignition, it might be safer using the normally closed/common contacts of a standard SPDT relay to provide the power to the sensor. Wire the coil with one side to ground, and the other to an accessory power line, and the relay will be energized whenever you have the car is running or in accessory position, removing power to the sensor.
Either that, or don't bother with the switch at all and just leave it powered up all the time, since the sensor output to your factory alarm trigger would be ignored when running anyway.
Posted By: techfiftyfive
Date Posted: October 30, 2005 at 11:28 PM
So there's no bad side effects if I kept the sensor powered on all the time, even while Im driving my car? One thing I can think of is the door light in my gauges turning on, thats only if glass breaks near the mic though, but still wouldnt bother me. Let me know if theres anything else though. Thanks
Posted By: dualsport
Date Posted: October 31, 2005 at 12:29 AM
Oh- were you planning on hooking these sensors up to your door switches? That's not going to work too well if the door switches are controlling the courtesy lights, because your sensor probably isn't going to be able to handle the current required for switching. If your alarm has a suitable trigger input, then it could work. If not, you may be best off putting in an aftermarket alarm with the capability.
Posted By: techfiftyfive
Date Posted: October 31, 2005 at 1:07 AM
Sending a (-) pulse to the light in my gauges that turns on whenever a door or when my trunk is opened, sets the factory alarm off and thats what I plan to use for the sensor. Aftermarket alarms are just pricey to me. I mean, if I could find one that I want (The Clifford 2way remote start/alarm with the LED remote not LCD) for a decent price, Id jump on it, but everywhere I look its at least $200.
Posted By: dualsport
Date Posted: October 31, 2005 at 1:28 AM
If you can check the (-) input you're planning to use as the trigger, find out how much current it draws when you connect an ammeter between it and ground. That would tell you beforehand if you might be overloading the sensor if you were to hook it up directly without a relay inline.
You probably should also add a relay to cut off power to the sensor when the ignition is off, to avoid the flickering of the gauge light while driving, if that's what you eventually tie in to.
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