I think I recognized an alarm call today while I was out in the back yard trying to get pictures of a red-breasted nuthatch. There are many juncos that frequent the area behind our house and quite a few of them were scattered in the open area near where I was standing. They would periodically all fly to the nearest cover for a few seconds before venturing back out into the open. On one occasion, I heard a fairly strident call right before they flew back to cover.