be on the lookout for
US /bi ɑn ðə ˈlʊkˌaʊt fɔr/
UK /bi ɑn ðə ˈlʊkˌaʊt fɔr/

1.
estar atento a, estar à procura de
to be actively watching or searching for something or someone
:
•
We need to be on the lookout for any suspicious activity.
Precisamos estar atentos a qualquer atividade suspeita.
•
The police are on the lookout for the escaped prisoner.
A polícia está à procura do prisioneiro foragido.