Reseting factory alarm, how to?

We have a 2010 Elantra all factory stock stereo, alarm, everything.

We lock the car in the garage at night and therefor do not set the alarm, last night I go down to get something out of the car, pop open the door and the alarm goes off.

A couple days ago my wife got out to put gas in the car, when she was done the keys were locked in the car.

I know some car alarms can be set to "auto arm" where is you turn off the car and walk away after a few minutes that car will automatically lock/set the alarm for you.

If that is a feature of the factory alarm I believe it has been activated.

Anyone know how to deactivate or change the factory alarm modes?

Thanks,
Scott