5 sentences

1. 他们处于警戒状态。

   tā​men chǔ​yú jǐng​jiè zhuàng​tài.

   They're on alert.

   Source: OpenSubtitles

2. 部队在边境地区加强了警戒。

   bù​duì zài biān​jìng dì​qū jiā​qiáng le jǐng​jiè.

   The troops stepped up their vigilance in the border region.

   Source: Dong Chinese Dictionary

3. 保持警戒！

   bǎo​chí jǐng​jiè!

   Stay alert!

   Source: OpenSubtitles

4. 由于敌军迫近，全城进入了警戒状态。

   yóu​yú dí​jūn pò jìn, quán chéng jìn​rù le jǐng​jiè zhuàng​tài.

   As the enemy forces approached, the entire city went into a state of alert.

   Source: Dong Chinese Dictionary

5. 我们应当警戒自己不要犯同样的错误。

   wǒ​men yīng​dāng jǐng​jiè zì​jǐ bù yào fàn tóng​yàng de cuò​wù.

   We should be on guard against making the same mistake again.

   Source: Dong Chinese Dictionary