We need to 'alert' the public 'to' the dangers of these chemicals. [=we need to tell the public about the dangers of these chemicals]
Several neighbors 'alerted' the authorities/police when they noticed strangers acting suspiciously.
The nurse kept/stayed 'alert' for any change [=watched for any change] in the patient's condition.
(..) I tried you on your cell phone. All we got was the message. - Oh, yeah? - What? You don't show up for lunch. Yeah, there was a terrorist alert-- - --In the subway. - Yeah. I'll just call everyone and apologize. - Hello? (..)2008 Two Lovers