caught unawares
To be surprised by someone or something. A: "Oh man, I was totally caught unawares when your mother showed up here this morning." B: "I figured as much when she told me that you answered the door in your robe and curlers!"
caught unaware(s)
surprised and unprepared. Sorry. You startled me when you came up behind me. I was caught unaware. The clerk was caught unawares, and the robber emptied out the cash register before the clerk could sound the alarm.