  Fluid instabilities are ubiquitous phenomena of great theoretical and applied
importance. In particular, an intriguing example is the thermocapillary or
B\'enard-Marangoni instability which occurs when a thin horizontal fluid layer,
whose top surface is free, is heated from below. In this phenomenon, after
passing a certain temperature difference threshold, the fluid develops a
regular pattern, usually hexagonal, of convection cells known as B\'enard
convection. In general this pattern is not visible to the naked eye unless
specific tracers are incorporated into the fluid. The use of thermal imaging is
a simple alternative not only for directly observing these phenomenon but also
for obtaining valuable quantitative information, such as the relationship
between the critical wavelength and the thickness of the fluid layer. Here, we
propose an experiment specially suited for laboratory courses in fluid
mechanics or nonlinear physics that involves the use of thermal cameras, or
appropriate smartphone accessories, to study B\'enard convection.
