  In this contribution we describe some interesting interplay between quantum
theory, general relativity and thermodynamics. In order to highlight the
connection between these theories, we describe two approaches that allow to
calculate thermal features as perceived by different observers in curved
spacetimes: the tunnelling method and the Unruh-DeWitt detector. In this
context, the semi-classical tunnelling approach is applied to the issue of
Hawking radiation and allows the calculation of the horizon temperature in a
wide variety of scenarios. The Unruh-DeWitt model is instead a quantum
field-theoretical approach that should give a more exact answer in terms of
transition rates between energy levels of an idealized detector.
