  Moving detectors in relativistic quantum field theories reveal the
fundamental entangled structure of the vacuum which manifests, for instance,
through its thermal character when probed by a uniformly accelerated detector.
In this paper, we propose a general formalism inspired both from signal
processing and correlation functions of quantum optics to analyze the response
of point-like detectors following a generic, non-stationary trajectory. In this
context, the Wigner representation of the first-order correlation of the
quantum field is a natural time-frequency tool to understand single-detection
events. This framework offers a synthetic perspective on the problem of
detection in relativistic theory and allows us to analyze various
non-stationary situations (adiabatic, periodic) and how excitations and
superpositions are deformed by motion. It opens up interesting perspective on
the issue of the definition of particles.
