Luvmymazda3

I have a 2011 Mazda3i I bought used about a year ago. A few days ago I was sitting at a red light when the alarm spontaneously triggered and I couldn't disarm it. I just had to drive with the lights flashing and the horn going until it quit on its own. It has not done this before and I hope it doesn't do it again! Anybody else have this happen?