  The Dimension-5 Seesaw Portal is a Type-I Seesaw model extended by $d=5$
operators involving the sterile neutrino states, leading to new interactions
between all neutrinos and the Standard Model neutral bosons. In this work we
focus primarily on the implications of these new operators at the GeV-scale. In
particular, we recalculate the heavy neutrino full decay width, up to
three-body decays. We also review bounds on the dipole operator, and revisit
LEP constraints on its coefficient. Finally, we turn to heavy neutrino pair
production from Higgs decays, where the former are long-lived and disintegrate
into a photon and a light neutrino. We probe this process by recasting two
ATLAS searches for non-pointing photons, showing the expected event
distribution in terms of arrival time $t_\gamma$ and pointing variable $|\Delta
z_\gamma|$.
