  We investigate the possibility of reproducing the recently reported
$3.55\,\mbox{keV}$ line in some simple decaying dark matter scenarios. In all
cases a keV scale decaying DM is coupled with a scalar field charged under SM
gauge interactions and thus capable of pair production at the LHC. We will
investigate how the demand of a DM lifetime compatible with the observed
signal, combined with the requirement of the correct DM relic density through
the freeze-in mechanism, impacts the prospects of observation at the LHC of the
decays of the scalar field.
