I have a factory alarm, you know that panic button thing, well anyways last night at around 3:30 am, the thing starts going off for no reason. I check to make sure no one is around, and see no other footprints in the snow. I'm still wondering why it went off. But then today I go to get gas and the guy tells me that I have no gas cap. Is it possible for someone to open the gas door, and set off the alarm? What sets off the alarm anyway?

Any door unlocked without the key or control will set off the alarm. It is possible the gas cap door is considered a "door" so if someone pried it open, it might set off the alarm.

If you had no gas cap, your check engine light should have come on, since the gas cap is part of the emissions system.

Should i be worried that the light hasn't gone on? When you open the gas door, its just the gas hole and thats it.

The missing gas cap is a two-trip failure. It's not surprising that the MIL didn't go on right away. It will be surprising if it fails to go on at all.

I believe that if the door is pryed open that the alarm will not go off or if the window is open and the latch can be reached. The doors, trunk and hood are the only things that set off the alarm as far as I know. As a matter of fact if your windows are rolled down with the alarm set and someone reaches inside and unlocks your door from the inside the alarm should also go off.

Shoot, I think the big question here is Why would anyone wana steal a gas cap? Doesn't make any sense to me. ???

I don't know...maybe the high gas prices got people to be very desperate and they came around and stole some of your premium gas you use in your Maxima *cough*

Did you check your gas levels?

i dunno, it was near the empty range before, so it wouldn't make a difference. But I stopped in at napa and got one for $10 so no big deal.

Make sure you get the exact gas cap. Because when I first got my car, I guess the previous owner had replaced the cap and got one for a Nissan but not specifically for a Maxima. SO my check engine light started coming on. I took it to the Nissan dealership and had them test it...I had the wrong gas cap. I think that, that is awesome that they can detect something so tedious!

I had my car broken into in the underground parking of my office a few months back. The thief broke the small quarter window on the passenger side. I opened the back door to throw my briefcase in and noticed a greeny thing hanging on the inside and it was the sheet of glass. The alarm tripped when the thief reached in to open the door handle and ran off. I tried this myself just to see what happens.
The thief picked my car probably because it looked good to him and thought that there were goodies stashed in the glove box and centre console. My back seat and floor were clean with no inticing objects laying about. Go figure...

I got a generic brand gas cap replacement. i went into napa to get one; they ran my car make/model/year into their computer, and got one that i guess was a perfect fit. And BTW The cap had been missing for some time and the light still didn't go off at all.

I was once missing a gas cap for about a month...
My "check engine" light never came on....