An alert guard stopped the robbers.机警的门卫拦住了劫匪。

The nurse kept/stayed alert for any change [=watched for any change] in the patient's condition.护士对病人病情的任何变化时刻保持警觉。

He was tired and had trouble staying alert while he was driving.他很疲倦，开车时无法保持警觉。

The nurse should be alert to any change in the patient's condition.护士应该对病人病情的任何变化都保持警觉。

He is alert to [=aware of] his duties as a father.他很清楚做父亲的责任。

They sounded an alert when enemy planes were approaching the city.敌机接近城市时，他们发出了警报信号。

Medical officials have put out an alert to hospitals to look out for the virus.卫生官员已向各家医院发出警告，要小心这种病毒。

The government has issued a terrorism/security alert.政府已发出恐怖袭击/安全警告。

We need to be on alert for any sudden changes.我们需要密切注意任何突发情况。

The attack could come at any time, so the soldiers need to be on full alert.进攻随时都有可能发生，因此士兵需要时刻保持高度警惕。

The recently flooded community is again on high alert as more rain is expected.预计更多的雨水将至，因此近期遭受洪涝灾害的地区再次处于高度戒备状态。

Several neighbors alerted the authorities/police when they noticed strangers acting suspiciously.几个邻居注意到一些鬼鬼祟祟的陌生人，立即报告了当局/警方。

The governor alerted island residents that a hurricane was coming.州长警告岛上居民飓风即将来临。

The teacher alerted the students that tests would be given the next day.老师提醒学生第二天要进行测验。

A friend recently alerted me to the existence of a new museum in my city.一个朋友最近提醒我说在我居住的城市有一座新的博物馆。

We need to alert the public to the dangers of these chemicals. [=we need to tell the public about the dangers of these chemicals]我们需要提醒公众注意这些化学制品的危险性。