  We analyze how the presence of closed timelike curves (CTCs) characterizing a
time machine can be discerned by placing a local particle detector in a region
of spacetime which is causally disconnected from the CTCs. Our study shows that
not only can the detector tell if there are CTCs, but also that the detector
can separate topological from geometrical information and distinguish periodic
spacetimes without CTCs (like the Einstein cylinder), curvature, and spacetimes
with topological identifications that enable time-machines.
