What would cause my car alarm to go off randomly in the middle of the night?

That I had tried disconnecting the sensor? Yes, I did. I am pretty sure it was even still disconnected when I brought it to them and they had to plug it back in. They didn't replace the hood switch. They said the hood was not aligned properly so they realigned it.

OK , , thank you for clearing that up. Next question , did they detail any other testing they did , and have you contacted them to let them know the current situation? One thing that might be helpful , is to stick with the same service adviser and technician for the current issue. Just so you know (not that it makes your wallet feel any better), some of these problems can be related to corrosion in a connector or ground and might be very difficult to trace until the symptom can be easily duplicated , very annoying when it involves an alarm! IF they give you a further diagnosis (whether or not it involves parts) ask them if they'll guarantee it.Not knowing other variables about your specific car such as collision/body work history and climate conditions , maint. etc. , it's hard to get any further into 'guessing' at the possibilities. I just hope for both yours and the techs' sake , it gets resolved quickly!

And my neighbor's sake ;) The dealer didn't tell me about any other testing they had done. They told me the problem "is usually tied to the hood sensor". Because they saw that the hood was misaligned, I don't think they looked any further. When I asked them how it could be the hood sensor if I disconnected it and the problem still continued, the tech didn't give me an answer and just repeated the explanation about the hood being out of alignment. I eventually asked to speak the service manager as I didn't feel like I was getting a good explanation. The service manager repeated the same explanation as the tech. I politely said "I don't understand how it can be the hood sensor if the problem continues when the hood sensor is disconnected". I think they felt I was being belligerent when I really was just trying to be logical and ensure that it was fixed. The service manager eventually told me that he couldn't fix what he couldn't see (in other words, the alarm would have to go off while it was there) and told me I was welcome to leave the car there until it went off. Since it had only gone off at night, I didn't think that would be very fruitful. It hasn't gone off since then until just the past 2 days and all of the times it has gone off are at night. At this point, I would be more than happy to just disengage the alarm permanently, but the dealer told me I cannot do that.

I feel bad , cause I know you'd like it fixed , like , yesterday, but as was said , the most likely way of finding the source/cause of the problem is to have it act-up. Only other thing I can think of , from past experience (on Hondas-not Hyundais ) is maybe a start would be to have info on where ALL ground connections to body are , and remove , check for corrosion and re-install them , any harness connectors or switch connectors with loose pin contact or corrosion could also be a source to check.I had one the customer decided to let stay with us , and it did take about a week of sitting(inside in a bay) for it to start acting up(yes at night!) Don't know what body control or security control software Hyundai has available to them for an '05 , but once I got some of the other items it couldn't be out of the way , I was able to narrow it down to basically either a faulty switch or intermittent high resistance. Based on my observations (pretty much looking useless , sitting in their van staring at a laptop searching for something to not be 'right' , I finally noticed that the pass. sliding door lock actuator was sluggish in response time compared to the others. only a little , but enough to make me curious. Pulled off the door panel and checked and found a ground wire covered in white powdery corrosion. Cleaned it re-attached it and problem solved. NOT an outright bad connection , as I stated before , just an increase in 'resistance' which apparently the drop in night temp. was enough to trigger a change in voltage , which is what the security system monitors. Just another one of my ways of saying , they might not be trying to rip you off , this really can be a tough one to tackle and does require patience AND persistence on both parts...............god I hope you stayed awake through all of this. good luck.