1. 警覺(jué)的；警惕的；留神的；機(jī)敏的
    If you are alert, you are paying full attention to things around you and are able to deal with anything that might happen.

    e.g. We all have to stay alert...
           我們大家都必須保持警惕。
    e.g. He had been spotted by an alert neighbour.
           一個(gè)警覺(jué)的鄰居發(fā)現(xiàn)了他。

2. 充分意識(shí)到…的;完全感覺(jué)到…的
    If you are alert to something, you are fully aware of it.

    e.g. The bank is alert to the danger.
           銀行充分意識(shí)到了危險(xiǎn)。

3. 警戒（狀態(tài)）；戒備（狀態(tài)）
    An alert is a situation in which people prepare themselves for something dangerous that might happen soon.

    e.g. Due to a security alert, this train will not be stopping at Oxford Circus.
           由于安全戒備的原因，該次列車(chē)在“牛津街口廣場(chǎng)”站將不停留。

4. 向…報(bào)警；使警覺(jué)；使警惕；使注意
    If you alert someone to a situation, especially a dangerous or unpleasant situation, you tell them about it.

    e.g. He wanted to alert people to the activities of the group...
           他想提醒人們小心該團(tuán)體的活動(dòng)。
    e.g. I was hoping he'd alert the police.
           我當(dāng)時(shí)希望他會(huì)報(bào)警。

5. see also: red alert

6. 處于警戒狀態(tài);保持戒備
    If soldiers or police are on alert, they are ready to deal with anything that may happen.

    e.g. Soldiers and police have been put on alert.
           士兵和警方都已進(jìn)入警戒狀態(tài)。

7. 準(zhǔn)備就緒；防備著
    If you are on the alert for something, you are ready to deal with it if it happens.

    e.g. They want to be on the alert for similar buying opportunities.
           他們希望隨時(shí)掌握有關(guān)類似購(gòu)買(mǎi)機(jī)會(huì)的信息。