  We study the coscattering mechanism in a simple Higgs portal which add two
real singlet scalars to the Standard Model. In this scenario, the lighter
scalar is stabilized by a single $\mathcal{Z}_2$ symmetry and acts as the dark
matter relic, whose freeze-out is driven by conversion processes. The heavier
scalar becomes an unstable state which participate actively in the
coscattering. We find viable parameter regions fulfilling the measured relic
abundance, while evading direct detection and big-bang nucleosynthesis bounds.
In addition, we discuss collider prospects for the heavier scalar as a
long-lived particle at present and future detectors.
