  An accelerated observer moving through empty space sees particles appearing
and disappearing, while an observer with a constant velocity does not register
any particles. This phenomenon, generally known as the Unruh effect, relies on
an initial vacuum state, thereby unifying the experience of all inertial
observers. We propose an experiment to probe this observer-dependent detector
response, using a laser beam in circular motion as a local detector of
superfluid helium-4 surface modes or third sound waves. To assess experimental
feasibility, we develop a theoretical framework to include a non-zero
temperature initial state. We find that an acceleration-dependent signal
persists, independent of the initial temperature. By introducing a
signal-to-noise measure we show that observing this signal is within
experimental reach.
