  Macroscopic concepts pertaining to the Unruh effect are elaborated and used
to clarify its physical manifestations. Based on a description of the motion of
accelerated, spatially extended laboratories in Minkowski space in terms of
Poincar\'e transformations, it is shown that, from a macroscopic perspective,
an accelerated observer will not register with his measuring instruments any
global thermal effects of acceleration in the inertial (Minkowskian) vacuum
state. As is explained, this result is not in conflict with the well-known fact
that microscopic probes respond non-trivially to acceleration if coupled to the
vacuum. But this response cannot be interpreted as the effect of some heat bath
surrounding the observer. It is also shown that genuine equilibrium states in a
uniformly accelerated laboratory cannot be spatially homogeneous. In
particular, these states coincide with the homogeneous inertial vacuum at
sufficiently large distances from the horizon of the observer and consequently
have the same (zero) temperature there. The analysis is carried out in the
theory of a free massless scalar field; however the conclusion that the Unruh
effect is not of a thermal nature, viz. induced by heat transfer, is generally
valid.
