on the qui vive
警惕地注意，随时准备应对可能的危险或意外情况
正式·描述高度警觉
英文释义
being on high alert or watchful for something
例句
The guards were on the qui vive for any sign of intruders.
典故来源
源自法语短语'qui vive?'（谁在？），哨兵询问口令时的警惕状态。