For native apps blacklist default emulator MSIN and similar attributes (and let the cat and mouse game begin).

For mobile web various fingerprinting techniques are available. As a fun (and quite irrelevant) example, you can immediately tell chrome, safari, firefox and node apart just with:

  atob('Ψ')
  x

I don't know. But I spent the better part of a day trying to prevent a game from detecting I was using an emulator.

Bluestacks in different configurations was among the things I tried.

Lost interest and decided the developers just don't want me as a potential customer.