  Recent research has indicated that negative energy fluxes due to quantum
coherence effects obey uncertainty principle-type inequalities of the form
$|\Delta E|\,{\Delta \tau} \lprox 1\,$. Here $|\Delta E|$ is the magnitude of
the negative energy which is transmitted on a timescale $\Delta \tau$. Our main
focus in this paper is on negative energy fluxes which are produced by the
motion of observers through static negative energy regions. We find that
although a quantum inequality appears to be satisfied for radially moving
geodesic observers in two and four-dimensional black hole spacetimes, an
observer orbiting close to a black hole will see a constant negative energy
flux. In addition, we show that inertial observers moving slowly through the
Casimir vacuum can achieve arbitrarily large violations of the inequality. It
seems likely that, in general, these types of negative energy fluxes are not
constrained by inequalities on the magnitude and duration of the flux. We
construct a model of a non-gravitational stress-energy detector, which is
rapidly switched on and off, and discuss the strengths and weaknesses of such a
detector.
