  We show that the particle-number distribution of diamond modes, modes that
are localized in a finite space-time region, are thermal for the Minkowski
vacuum state of a massless scalar field, an analogue to the Unruh effect. The
temperature of the diamond is inversely proportional to its size. An inertial
observer can detect this thermal radiation by coupling to the diamond modes
using an appropriate energy-scaled detector. We further investigate the
correlations between various diamonds and find that entanglement between
adjacent diamonds dominates.
