Passive alarm?

We've owned our 2005 Sedona for almost a month now. Twice the car has failed to start when using the correct key. My wife is now on a trip to South Carolina with it and she's been stuck for the past 24 hours. She had the van towed back to where she was staying because it wouldn't start. All she got was a strange dinging noise. The next morning the van started right up. We had a mechanic look it over and he said the starter is fine. Is it possible there is an alarm on the van that is shorting out? Is there a way to deactivate the alarm if there is one?