Usage Note
Alertar takes the preposition sobre or de for the topic of the warning: alertar sobre un peligro, alertar de la situación. It can also be used reflexively (alertarse) to mean 'to become alarmed'. The adjective alerta is invariable for gender and number in its predicative use: estar alerta.
Examples
"Las autoridades alertaron a la población."
Natural Translation
The authorities alerted the population.

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