  One of the foremost concern in the analysis of quantum gravity is whether the
locations of classical horizons are stable under a full quantum analysis. In
principle, any classical description, when interpolated to the microscopic
level, can become prone to fluctuations. The curious question in that case is
if there indeed are such fluctuations at the Planck scale, do they have any
significance for physics taking place at scales much away from the Planck
scale? In this work, we try to attempt the question of small scales and address
whether there are definitive signatures of Planck scale shifts in the horizon
structure. In a recent work (arXiv:2107.03406), it was suggested that in a
nested sequence of Rindler causal wedges, the vacua of preceding Rindler frames
appear thermally populated to a shifted Rindler frame. The Bogoliubov analysis
used relies on the global notion of the quantum field theory and might be
unable to see the local character of such horizon shifts. We investigate this
system by means of the Unruh-DeWitt detector and see if this local probe of the
quantum field theory is sensitive enough to the shift parameters to reveal any
microscopic effects. For the case of infinite-time response, we recover the
thermal spectrum, thus reaffirming that the infinite-time response probes the
global properties of the field. On the other hand, the finite-time response
turns out to be sensitive to the shift parameter in a peculiar way that any
detector with energy gap $\Omega c/a \sim 1$ and is operational for time scale
$T a/c \sim 1$ has a measurably different response for a macroscopic and
microscopic shift of the horizon, giving us direct probe to the tiniest
separation between the causal domains of such Rindler wedges. Thus, this study
provides an operational method to identify Planck scale effects which can be
generalized to various other interesting gravitational settings.
