be on to (someone)

be on to (someone)

1. To have knowledge, be suspicious, or be aware of someone's actions, behavior, or intention. You'd better tread carefully, I'm on to you now. The police are on to us! Everybody run!
2. To be in contact with someone at a given point in time. I'll be on to you tomorrow about the details of our meeting. I was on to John yesterday about where he wants to go for his birthday.
See also: on

be on to

1. Be aware of or have information about, as in They can't pull that trick again; we're on to them now. [Colloquial; second half of 1800s]
2. Discover something important or profitable, as in The researchers claim they are really on to something big. [Colloquial; mid-1900s]
See also: on

be on to someone

be close to discovering the truth about an illegal or undesirable activity that someone is engaging in. informal
See also: on, someone

be ˈonto somebody


1 (informal) know about what somebody has done wrong: She knew the police would be onto them.
2 (also get ˈonto somebody) be talking to somebody, usually in order to ask or tell them something: They’ve been onto me for ages to get a job.I must get onto the local council about all the rubbish in the street.
See also: somebody

be on to

Informal
To be aware of or have information about: You'll never deceive us again; we're on to you.
See also: on