  We investigate two models of measuring devices designed to detect a
non-relativistic free particle in a given region of spacetime. These models
predict different probabilities for a free quantum particle to enter a
spacetime region $R$ so that this notion is device dependent. The first model
is of a von Neumann coupling which we present as a contrast to the second
model. The second model is shown to be related to probabilities defined through
partitions of configuration space paths in a path integral. This study thus
provides insight into the physical situations to which such definitions of
probabilities are appropriate.
