警戒严密的

例句：

1. 1. The police are keeping a close watch on the suspects.
   警方正在密切监视嫌疑人。
2. 2. He is always vigilant about his safety.
   他总是非常警惕自己的安全。
3. 3. The soldiers were all on guard duty at the border.
   士兵们都在边境执行守卫任务。