  Several approaches to quantum gravity suggest violations of Lorentz symmetry
as low-energy signatures. This article uses a concrete Lorentz-violating
quantum field theory to study different inertial vacua. We show that they are
unitarily inequivalent and that the vacuum in one inertial frame appears, in a
different inertial frame, to be populated with particles of arbitrarily high
momenta. At first sight, this poses a critical challenge to the physical
validity of Lorentz-violating theories, since we do not witness vacuum
excitations by changing inertial frames. Nevertheless, we demonstrate that
inertial Unruh-De Witt detectors are insensitive to these effects. We also
discuss the Hadamard condition for this Lorentz-violating theory.
