  Modeling of rare neutrino processes often relies on either simple
approximations or expensive detector simulations. The former is often not
sufficient for interactions with complex morphologies, while the latter is too
time-intensive for phenomenological studies. We present SIREN (Sampling and
Injection for Rare EveNts), a new tool for neutrino phenomenology and
experimental searches alike that enables accurate interaction and detector
geometry modeling without the overhead of detailed detector response
simulations. SIREN handles the injection of rare process final states and the
associated weighting calculations with the speed needed for phenomenological
investigations and the detail necessary for dedicated experimental searches.
The extensible design of SIREN allows it to support a wide range of
experimental designs and Beyond-Standard-Model neutrino interactions. Users
need only specify the physical process, detector geometry, and initial neutrino
flux under consideration before they can accurately simulate a model in their
detector of choice. We demonstrate the capability of SIREN through two
examples: (1) Standard Model $\nu_\mu$ deep inelastic scattering in IceCube,
DUNE, and ATLAS; and (2) heavy neutral lepton interactions in MiniBooNE,
MINER$\nu$A, CCM. A variety of detector geometry descriptions, interaction
cross sections, and neutrino fluxes are also provided for users to get started
with immediately.
