  We analyze a quantum version of the weak equivalence principle, in which we
compare the response of a static particle detector crossed by an accelerated
cavity with the response of an accelerated detector crossing a static cavity in
(1+1)-dimensional flat spacetime. We show, for both massive and massless scalar
fields, that the non-locality of the field is enough for the detector to
distinguish the two scenarios. We find this result holds for vacuum and excited
field states of different kinds and we clarify the role of field mass in this
setup.
