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---

>> (44 15' N - Elevation 1580')
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On Dec 17, 6:16pm, snipped-for-privacy@webtv.net (---MIKE---) wrote:

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?
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Hyundaitech asked,

2008 Elantra.
---MIKE---

>> (44 15' N - Elevation 1580')
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On Dec 18, 7:56am, snipped-for-privacy@webtv.net (---MIKE---) wrote:

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.
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hyundaitech wrote:

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---

>> (44 15' N - Elevation 1580')
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On Dec 20, 12:29pm, snipped-for-privacy@webtv.net (---MIKE---) wrote:

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.
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