Have one's number Verb + object/complement informal
To understand someone or something, so you can predict what they/it will do and deal with or defeat them/it
I know what they're going to do because I have their number.
He thought he can fool me again, but I have his number.
The verb "have" should be conjugated according to its tense.
The origin is unclear, but the source said that It came from in the mid-1800s, and the earliest version was used by Charles Dickens in his novel, Bleak House in 1853.