alert

alert adjective uk/əˈlɜːt/ us
quick to notice and react to things around you

бдительный
A young dog should be alert and playful. Teachers need to be alert to sudden changes in students' behaviour. alert ness noun [ U ]

бдительность

alert verb [ T ] uk/əˈlɜːt/ us
to warn someone of a possibly dangerous situation

предупреждать
Six hours later she still wasn't home so they alert ed the police.

ALERT noun

uk/əˈlɜːt/ us
[ C ] a warning about a possibly dangerous situation

тревога
a bomb alert
 be on full/red alert
to be expecting problems and ready to deal with them

быть в состоянии боевой готовности
Police in the region were on full alert against further attacks.