We will discuss how relativistic causality and covariance play a role in the measurement problem in quantum fields and even in our ability to put information into a quantum field. We will compare the Fewster-Verch formalism with the Unruh-DeWitt-like (UDW) particle detector models. We will discuss the limitations of both measurement frameworks as well as the typical abuses that are often made with Unruh-DeWitt-like detector models and how they matter in general relativistic scenarios. Finally we will discuss the claim in [arXiv:2103.13400] that weakly coupled detectors cannot harvest entanglement and show what is the effect of that claim, if any, on the feasibility of entanglement harvesting with particle detectors.