  In the Standard Model (SM) of particle physics, the branching ratio for Higgs
boson decays to a final state which is invisible to collider detectors, $H
\rightarrow ZZ^{\star} \rightarrow \nu \bar{\nu} \nu \bar{\nu}$, is order
0.10%. In theories beyond the SM (BSM), this branching ratio can be enhanced by
decays to undiscovered particles like dark matter (DM). At the Large Hadron
Collider (LHC), the current best upper limit on the branching ratio of
invisible Higgs boson decays is 11% at 95% confidence level. We investigate the
expected sensitivity to invisible Higgs decays with the Silicon Detector (SiD)
at the International Linear Collider (ILC). We conclude that at $\sqrt{s}=250$
GeV with 900 fb$^{-1}$ integrated luminosity each for $e_{L}^-e_{R}^+$ and
$e_{R}^-e_{L}^+$ at nominal beam polarization fractions, the expected upper
limit is 0.16% at 95% confidence level.
