This is the 3876th most frequent French word.
alerté
Warned or alerted.
In this sentence, 'alerté' is used as the past participle of the verb 'alerter' in its conjugated form, indicating the act of informing or warning someone about a potential risk.
J'ai alerté ma collègue du danger qui approchait.
I alerted my colleague of the approaching danger.
Here, 'alerté' functions in the passive voice, indicating that the subject of the sentence has received the alert.
Il semble qu'il ait été alerté à temps pour éviter l'accident.
It seems he was alerted in time to avoid the accident.
In this case, 'alertés' is plural to agree with the plural subject 'les habitants' and describes their state as having received the alert due to the sirens.