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

1.
留意, 搜尋
to be actively watching or searching for something or someone
:
•
We need to be on the lookout for any suspicious activity.
我們需要留意任何可疑活動。
•
The police are on the lookout for the escaped prisoner.
警方正在搜捕越獄的囚犯。