警戒的英文：
warn
be alert for

参考例句：

Radar warning coverage
雷达警戒范围

The police have been instructed to keep an eye out for pickpockets at the fair.
遵照指示，警察在展览会期间警戒小偷。

The commander called in the second battalion's outposts.
指挥官下令第二营警戒部队撤回。

The police cordon off the area to prevent loot.
警察用警戒围住该地区以防抢劫。

The outlying sonar picket.was to detect,localize,and engage any submarine trying to close the convoy(Tom Clancy)
外部声纳警戒队的任务是…发现、定位和掌握任何企图靠近护卫舰的潜水艇(汤姆·克兰西)

Have one's eyes wide open; be careful
监视;警戒

On one's guard; on the watch
警戒着;守望

Watch out for; be on the lookout for
守望;警戒;留意;防备

Picket ship
雷达警戒船

Extremely observant;vigilant.
非常机警的;警戒的

warn是什么意思：
v. 警告；告诫；提醒；预告

They warned him to be careful.
他们告诫过他要小心。

Seismal Microcosmic Warning Signs
地震微观前兆

She yelled a warning to us.
她大声警告我们。

They attacked without a warning.
他们不宣而战。

The police are warning of possible delays.
警方通知交通可能受阻。

alert是什么意思：
adj. 警觉的；思维敏捷的
v. 向…报警；使警觉，使意识到
n. 警戒，警惕；警报

Suddenly the combat alert sounded.
突然战斗警报响了。

conflict alert (CA)
碰撞警告

She was very brisk and alert.
她完全是一副干脆利落、精神抖擞的神情。

They have put the army on the alert.
他们已使军队进入戒备状态。

Don't alert the enemy.
不要惊动敌人。