I posted this on the electronics forum but no replies; thought I would ask here too. If this question shouldn't be posted here the moderators can feel free to delete it; I'm just looking for help.

Looking for ideas because I'm stumped - a couple of weeks ago in the middle of the night I woke up to the sound of my car alarm (horn sounding and headlights flashing); I quickly grabbed my key fob and clicked the open lock a couple times and it stopped, however the next night it did it again, and then 20 minutes later again. nothing bothering it, it's just sits in the driveway without anything touching it. I checked all the bulbs including the one in the trunk to make sure they're all working, my key fob batteries are good, I haven't tested my car battery but it seems to have plenty of power when starting. I even pulled the fuse under the hood labeled horn alarm. I ended up unhooking the battery for about five minutes; seemed to do the trick for about three days then it started again. did it twice this morning; not sure what to do. Any ideas? Driving my neighbors crazy.......

 

Others here may have better ideas but I suggest you focus on the switches that can set off the alarm. Door switches, hood & trunk (?). With some digging you may find something either out of adjustment or a failing wire or ...?
Here's the FSM on the subject - thanks to NICO club:
http://www.nicoclub.com/manuals/G37/Sedan/2013/SEC.pdf

 

Also how many keys do you have. I had a bad key that was the culprit to the alarm going off due to an issue with the panic on the fob.

 

OK thanks; I'll look into those things

 

I realize this thread is 2+ years old, but found it as I was searching for the exact same issue with my 2013 and it might help someone else out now or later.
As Skyline stated, it is indeed an intermittent issue with a sensor, mine happens to be the hood. After replacing the batteries in both FOB's didn't change a thing, I tracked it down only because I have the mobile Drone remote start app that shows open/close status of doors/hood/trunk.
After a day or two of monitoring their status whenever the alarm would randomly sound, I noticed the hood would show open on the Drone app for no reason. Also the Drone remote start will advise of successful and unsuccessful remote starts, and it wasn't starting due to the hood being open.
So if anyone out there is having the same issue, "hood open" is a good place to begin trying to figure out why it's open when it's not! LOL

 

Now it's even older but I have this problem. It's great to know this could be a hood sensor issue--but what do you do about it?

 

I'm older too! Depending on what year your car is, I think the hood switch used to be separate from the actual locking mechanism but then became part of it in later years. (Guessing on that one.) But I'm pretty sure these switches indicate open doors, hood and trunk by connecting to ground when open. So if you can physically get to them you should be able to disconnect a suspect switch and temporarily take it out of the circuit. If that were to stop the random alarm problem then you'd have your answer.

 

IT's a 2009. I will see if I can find the switch. I looked at a vid for a G35 but I imagine the design is similar. Will post back on success.

 

The switch is integrated into the passenger-side hood latch. Once you locate it, press it a few times with your finger. There should be a solid click each time.

 

This could be part of the problem. I noticed the hood fit on the passenger side was misaligned when the hood is closed so I looked into that. The passenger side hood latch does not lock in the closed position when the hood is closed so the hood is not pulled all the way down on that side (about 1/2 inch out of fit). I haven't opened the latch cover plate yet to see why. I didn't see the sensor switch, but I'll look again with this in mind.

My son just bought this car a couple of weeks ago so we are still discovering things like this here and there.

 

(I am doing this via mobile so bear with me)
Here is a pic of the latch and the microswitch- just for reference:

If the hood is not properly latching then the switch is not making proper contact.

Temporarily, you could just unplug the connector until you resolve the hood closing issue.

Also, welcome to the forum. When you/ your son have time, download a copy of the factory shop manual (FSM) from here. This will have everything you need to work on these cars.

 

That is great, and almost certainly the issue. Thanks very much.

I found the FSM through other searches. It's been a long time since I've done any work on a car. I used to do some basic stuff to my car and motorcycle (oil changes, timing, valve clearances, other tune-up type stuff) before all of the new technology (I'm talking 1980s) and some of the stuff in this manual assumes skills and knowledge that are over my head. Anyway, some helpful stuff in there.

 

BTW I am new to this forum and I see this is a sedan subforum, and this car is a convertible (also a subforum for that). Sorry for the misplaced post but the problem and solution seem to be the same across the board.

 

Same thing happened to me on my 2010 this is a old thread but f it does this happens if you leave the car unlocked too?

 

Not for me, only when it was locked.

Replacing the hood latch fixed the problem.