  Beauty and charm e+e- factories running at resonance thresholds have unique
capabilities for studies of the production of light Dark Matter particles in
the decays of B_q (D) meson pairs. We provide a comprehensive study of light
Dark Matter production in heavy meson decays with missing energy in the final
state, such as B_q (D^0) -> "missing energy" and B_q (D^0) -> \gamma + "missing
energy". We argue that such transitions can be studied at the current flavor
factories (and future super-flavor factories) by tagging the missing-energy
decays with B_q (D^0) decays "on the other side".
