Quantum fields on curved spacetimes can be described in terms of nets of \(C^*\) algebras. It is interesting to inquire whether the corresponding net structure incorporates some information on the underlying spacetime geometry. The paper under consideration presents some interesting results on that score, concentrating on information on the causal structure of spacetimes. In particular, it is shown that a net isomorphism on a globally hyperbolic spacetime induces a conformal transformation of the underlying spacetime, provided that some technical conditions are satisfied. The case of a free Klein-Gordon field is treated in some detail.