  We address quasinormal modes of compact objects in several alternative
theories of gravity. In particular, we focus on black holes and neutron stars
with scalar hair. We consider black holes in dilaton-Einstein-Gau\ss -Bonnet
theory, and in a generalized scalar-Einstein-Gau\ss -Bonnet theory. In the
latter case scalarized black holes arise, and we study the stability of the
different branches of solutions. In particular, we discuss how the spectrum of
quasinormal modes is changed by the presence of a non-trivial scalar field
outside the black hole horizon. We discuss the existence of an (effective)
minimum mass in these models, and how the spectrum of modes becomes richer as
compared to general relativity, when a scalar field is present. Subsequently we
discuss the effect of scalar hair for realistic neutron star models. Here we
consider $R^2$ gravity, scalar-tensor theory, a particular subsector of
Horndeski theory with a non-minimal derivative coupling, and again
dilatonic-Einstein-Gau\ss -Bonnet theory. Because of the current lack of
knowledge on the internal composition of the neutron stars, we focus on
universal relations for the quasinormal modes, that are largely independent of
the equations of state and thus the matter content of the stars.
