have somebody's number

have (got) (one's) number

To understand or know someone or something well enough to anticipate what they will do. That team is impossible to beat—they've had our number since 2006! Oh, don't worry, I've got his number—he's a typical brat. She caught me by surprise last time, but I've got her number now, and I won't let her manipulate us again.

have somebody’s ˈnumber

(informal) really understand what type of person somebody is and what they plan to do: Don’t worry, I’ve got his number. I shall be very careful in any business I do with him. ♢ You can’t fool me, you know. I’ve got your number.