Agree. Just keep walking, and act like you've done nothing wrong (because you haven't). Happens to me all the time; I've only had someone say something once. In that instance, another clerk who saw me come in just said "oh, it did that when he came in, don't worry about it".
I've often entertained the idea of running like crazy when it goes off; if I didn't have a bad knee, I'd probably try it.
I was pushing a cart out of Target with a large flat screen TV last week; beep beep beep, nobody said nuthin.
