人的狀態：眼睛睜著
這一組是塔上那個人本身。形容詞的 alert 都在描述同一個身體狀態：沒有放鬆、注意力朝外、隨時可以動——差別只在他警覺的是「周遭」、是「腦子轉得快」，還是「某一件特定的危險」。
watchful · adjective · C1
Watching and listening carefully, ready to notice or act on anything that happens.
警覺的 / 專注的
核心畫面
Picture the one person standing high up on the lookout tower while everyone else sleeps. Nothing has happened yet — that is the point. Their eyes are open, their body is turned outward, and they are ready to shout the moment something moves on the horizon. Every use of `alert` keeps a piece of that : the person who is watching, the shout they give, and the state a whole town is in once the shout has gone out.
可以想成一個人站在瞭望塔上，其他人都在睡。此刻什麼事都還沒發生——這正是重點。他眼睛睜著、身體朝著外面，只要地平線上…更多收起
可以想成一個人站在瞭望塔上，其他人都在睡。此刻什麼事都還沒發生——這正是重點。他眼睛睜著、身體朝著外面，只要地平線上有東西一動，他隨時可以喊出來。alert 的每一種用法都留著這個守望者的某一塊：那個看著的人、他喊出來的那一聲、以及整座城鎮聽到之後進入的那個狀態。所以這個字從頭到尾都不是「已經出事了」，而是「還沒出事，但我準備好了」。From the word’s history
From French alerte (17c.), from the phrase a l'erte, "on the watch", from Italian all'erta, literally "to the height" — erta being a lookout or high tower (ultimately from Latin erigere, "to raise"). It entered English as an adverb in the 1610s meaning "on the watch", became an adjective by 1712, a noun in 1796 ("attitude of vigilance", as in on the alert) and then "a warning report" by 1803, and a verb by 1864. The English phrase on the alert is a direct fossil of the original Italian all'erta — literally, up on the lookout tower.
alert 來自法語 alerte（17 世紀），源頭是片語 a l'erte「在守望中」，而這又來自義大利語 all'erta，字面意思是「到高處去」——erta 指的是瞭望點、高塔（最終來自拉丁語 erigere「升起」）。它進入英文的順序很清楚：1610 年代先是副詞「在守望著」，1712 年成為形容詞，1796 年變成名詞（指「戒備的狀態」，也就是 on the alert 這個說法），1803 年才多出「警報」的意思，1864 年再成為動詞。所以英文的 on the alert 其實就是義大利語 all'erta 的化石：字面上真的是「站在瞭望塔上」。
Online Etymology Dictionary, entry "alert" (etymonline.com/word/alert)
Three branches
喊出去：把警覺傳給別人
動詞是塔上那個人開口的那一刻。他把自己已經有的警覺送到別人身上，讓原本不知情的人也進入戒備——所以 alert 當動詞時，受詞永遠是「人」，不是「危險」。
warn officially · verb · C1
To warn someone officially about a problem or danger so they can get ready.
通報 / 示警
喊完之後：警報與戒備
名詞是那一聲喊本身，以及喊完之後整個地方停留的狀態。這一組把守望者的畫面從「一個人」放大成「一套制度」：颱風警報、空襲警報、醫院的戒備等級，都是把塔上那一聲固定下來的結果。
a warning · noun · C1
A warning that tells people to be ready for possible danger.
警報
原始詞典資料10 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
Alertname
- 1
A community in the Qikiqtaaluk Region, Nunavut, Canada; the northernmost permanently inhabited place in the world.
- 2
An alternative name for Alharod, a village in Varzaqan County, East Azerbaijan Province, Iran.
- 3
An unincorporated community in Jackson Township, Decatur County, Indiana, United States.
alertadj詞源 1/əˈlɜːt/
- 1
Attentive; awake; on guard.
- 2
obsoletebrisk; nimble; moving with celerity.
- I saw an alert young fellow that cocked his hat upon a friend of his who entered just at the same time with myself
alertnoun詞源 1/əˈlɜːt/
- 1
An alarm.
- 2
A notification of higher importance than an advisory.
- 3
governmentmilitarypoliticsA state of readiness for potential combat.
- an airborne alert; ground alert
- 4
computingengineeringmathematicsSynonym of bell (“bell character”).
alertverb詞源 2/əˈlɜːt/
- 1
To give warning to.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。