tip someone off
phrasal verb with tip verb uk/tɪp/ us/tɪp/ -pp-
C2 向（某人）告密;给（某人）通风报信
to warn someone secretly about something that will happen, so that they can take action or prevent it from happening
[ + that ] Somebody must have tipped the burglars off that the house would be empty. 一定是有人给盗贼通风报信，告诉他们房子里到时候会没有人。
The robber was caught when someone tipped off the police. 有人向警方报信后，抢劫者即被抓获。