Adult females have a reputation for making a "wac-wac" call when alarmed around the nest (a type of double squawk that is also described as "barking.") We only observed it a precious few times last year in the owlets, and honestly, the first time I heard it I was certain it was something other than an owl. I had no idea an owlet could or would make this vocalization.
Ruby made the same call today at about 12:40 PM, so we have good color video of her doing it. Perhaps the owlets make more different types of vocalizations when there aren't adults around to make them instead.