be on to(redirected from on to us)
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]
be on toInformal
To be aware of or have information about: You'll never deceive us again; we're on to you.