We explore signals of new physics with two Higgs bosons and large
missing transverse energy at the LHC. Such a signature is characteristic of
models for dark matter or other secluded particles that couple to the
standard model through an extended scalar sector. Our goal is to provide
search strategies and an interpretation framework for this new signature that
are applicable to a large class of models. To this end, we define simplified
models of hidden sectors leading to two different event topologies: symmetric
decay, i.e., pair-produced mediators decaying each into a Higgs plus
invisible final state; and di-Higgs resonance, i.e., resonant Higgs-pair
production recoiling against a pair of invisible particles.