  We study Extreme Mass Ratio Inspirals (EMRIs), during which a small body
spirals into a supermassive black hole, in gravity theories with additional
scalar fields. We first argue that no-hair theorems and the properties of known
theories that manage to circumvent them introduce a drastic simplification to
the problem: the effects of the scalar on supermassive black holes, if any, are
mostly negligible for EMRIs in vast classes of theories. We then exploit this
simplification to model the inspiral perturbatively and we demonstrate that the
scalar charge of the small body leaves a significant imprint on gravitational
wave emission. Although much higher precision is needed for waveform modelling,
our results strongly suggest that this imprint is observable with LISA,
rendering EMRIs promising probes of scalar fields.
