Unexpected alarm

Today I went into my chiropractor's office for about twenty minutes. I
did not lock the car. When I came out I opened the door and the horn
started beeping. This happened once before. What would cause this?
The temperature was below zero F. Would this be a factor?


---MIKE---

 

Not sure why this would have occurred. Typically the alarm will not
arm if the doors are not locked or the hood is not shut. What year
and model vehicle is this?

 

Hyundaitech asked,

2008 Elantra.


---MIKE---

 

I don't recall the specifics, but this is new enough that it may be
possible to program the BCM to allow alternate ways of arming the
alarm such as key lock and lock button. I'd still think the doors
should be locked, though.

 

Sometimes I only leave the car for a couple of minutes such as getting
trash out of the trunk at the dump. It makes no sense to lock the door
then.


---MIKE---

 

I meant that if the alarm was armed, it's odd that the doors weren't
locked, not that you intended to lock them. Under normal
circumstances, the alarm won't arm unless the doors are locked.