  We analyze the phase transition in improved holographic QCD to obtain an
estimate of the gravitational wave signal emitted in the confinement transition
of a pure SU(3) Yang-Mills dark sector. We derive the effective action from
holography and show that the energy budget and duration of the phase transition
can be calculated with minor errors. These are used as input to obtain a
prediction of the gravitational wave signal. To our knowledge, this is the
first computation of the gravitational wave signal in a holographic model
designated to match lattice data on the thermal properties of pure Yang-Mills.
