Child support

Good morning.
Currently my ex-wife is not working and I’m paying child support. When she goes back to work I don’t believe she’ll notify me. How can I find out when she goes back work in order for child support to be recalculated? What if she and the children move out of state, how can I know if she has gone back to work? Again, I don’t believe she’ll notify me when she goes back to work.

Thank you for your time

You may hire a PI to check up on her.