They are on the watch.

他们小心警戒。

Be on the watch for thieves in this crowd.

在这些人群中要提防有小偷。

The police were on the watch for any trouble.

警察局提防出现任何乱子。

The conductor was always on the watch for such doings.

这个指挥总是提防这样的动作。

Why is the third hand on the watch called a second hand?

手表上的第三只针为什么叫做秒针(第二只针)？