  We investigate the polarization modes of gravitational waves in $f(Q)$
non-metric gravity without gauge fixing. The main result of this study is that
no further scalar mode appears more than the two standard plus and cross
transverse polarizations of massless tensor gravitational radiation, typical of
General Relativity. This is because the first-order perturbation of connection
does not modify the linearized field equations in vacuum which remain gauge
invariant. Then, the world line equations of free point particles, as well as
the equations of their deviations, are obtained using only the symmetric
teleparallel connection. In $f(Q)$ gravity, test masses follow timelike
geodesics and not autoparallel curves. In the proper reference frame, thanks to
the geodesic deviation equation of the structure-less bodies in free fall, we
prove that, in any gauge, only the metric perturbations $h_{\mu\nu}$, related
to tensor modes, survive by exploiting the gauge invariance. Besides, scalar
modes disappear. This allows us to conclude that only two degrees of freedom of
linearized $f(Q)$ non-metric gravity propagate as in General Relativity and in
$f(T)$ teleparallel gravity. The situation is different with respect to $f(R)$
gravity (with $f(R)\neq R$) where a further scalar mode is found.
