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.
(..) Keep up! (HORSE NEIGHS) (HORSE NEIGHS) Stay straight! MAN: Keep your colors held high! MAN : Stay alert! (SPITS) (HORSE GRUNTING) (HORN BLOWING) Ha! (HORSE NEIGHS) (..)2017 TvShow: Vikings Title: On the Eve Season: 4 Episode 19
(..) Not for me. I am dead anyway. Perhaps they will spare you. (GASPING) I was paid by King Harald Finehair. MAN: Stay alert! Hold the line! Line! Push on! Pull up on the rear! Hold your form! (..)2017 TvShow: Vikings Title: On the Eve Season: 4 Episode 19